| publicationDate,title,abstract,id | |
| 2017-01-16,Electric field modulation of the non-linear areal magnetic anisotropy energy,"We study the ferromagnetic layer thickness dependence of the | |
| voltage-controlled magnetic anisotropy (VCMA) in gated CoFeB/MgO | |
| heterostructures with heavy metal underlayers. When the effective CoFeB | |
| thickness is below ~1 nm, the VCMA efficiency of Ta/CoFeB/MgO heterostructures | |
| considerably decreases with decreasing CoFeB thickness. We find that a high | |
| order phenomenological term used to describe the thickness dependence of the | |
| areal magnetic anisotropy energy can also account for the change in the areal | |
| VCMA efficiency. In this structure, the higher order term competes against the | |
| common interfacial VCMA, thereby reducing the efficiency at lower CoFeB | |
| thickness. The areal VCMA efficiency does not saturate even when the effective | |
| CoFeB thickness exceeds ~1 nm. We consider the higher order term is related to | |
| the strain that develops at the CoFeB/MgO interface: as the average strain of | |
| the CoFeB layer changes with its thickness, the electronic structure of the | |
| CoFeB/MgO interface varies leading to changes in areal magnetic anisotropy | |
| energy and VCMA efficiency.",1701.04150v1 | |
| 2018-10-01,Determination of spin Hall angle in heavy metal/CoFeB-based heterostructures with interfacial spin-orbit fields,"Magnetization dynamics in W/CoFeB, CoFeB/Pt and W/CoFeB/Pt multilayers was | |
| investigated using spin-orbit-torque ferromagnetic resonance (SOT-FMR) | |
| technique. An analytical model based on magnetization dynamics due to SOT was | |
| used to fit heavy metal (HM) thickness dependence of symmetric and | |
| antisymmetric components of the SOT-FMR signal. The analysis resulted in a | |
| determination of the properties of HM layers, such as spin Hall angle and spin | |
| diffusion length. The spin Hall angle of -0.36 and 0.09 has been found in the | |
| W/CoFeB and CoFeB/Pt bilayers, respectively, which add up in the case of | |
| W/CoFeB/Pt trilayer. More importantly, we have determined effective interfacial | |
| spin-orbit fields at both W/CoFeB and CoFeB/Pt interfaces, which are shown to | |
| cancel Oersted field for particular thicknesses of the heavy metal layers, | |
| leading to pure spin-current-induced dynamics and indicating the possibility | |
| for a more efficient magnetization switching.",1810.00641v1 | |
| 2011-07-01,"High frequency magnetic behavior through the magnetoimpedance effect in CoFeB/(Ta, Ag, Cu) multilayered ferromagnetic thin films","We studied the dynamics of magnetization through an investigation of the | |
| magnetoimpedance effect in CoFeB/(Ta, Ag, Cu) multilayered thin films grown by | |
| magnetron sputtering. Impedance measurements were analyzed in terms of the | |
| mechanisms responsible for their variations at different frequency intervals | |
| and the magnetic and structural properties of the multilayers. Analysis of the | |
| mechanisms responsible for magnetoimpedance according to frequency and external | |
| magnetic field showed that for the CoFeB/Cu multilayer, ferromagnetic resonance | |
| (FMR) contributes significantly to the magnetoimpedance effect at frequencies | |
| close to 470 MHz. This frequency is low when compared to the results obtained | |
| for CoFeB/Ta and CoFeB/Ag multilayers and is a result of the anisotropy | |
| distribution and non-formation of regular bilayers in this sample. The MImax | |
| values occurred at different frequencies according to the used non-magnetic | |
| metal. Variations between 25% and 30% were seen for a localized frequency band, | |
| as in the case of CoFeB/Ta and CoFeB/Ag, as well as for a wide frequency range, | |
| in the case of CoFeB/Cu.",1107.0204v1 | |
| 2023-01-12,Cryogenic temperature deposition of high-performance CoFeB/MgO/CoFeB magnetic tunnel junctions on 300 mm wafers,"We developed a cryogenic temperature deposition process for high-performance | |
| CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) on 300 mm thermally oxidized | |
| silicon wafers. The effect of the deposition temperature of the CoFeB layers on | |
| the nanostructure, magnetic and magneto-transport properties of the MTJs were | |
| investigated in detail. When CoFeB was deposited at 100 K, the MTJs exhibited a | |
| perpendicular magnetic anisotropy (PMA) of 214 uJ/m2 and a voltage-controlled | |
| magnetic anisotropy (VCMA) coefficient of -45 fJ/Vm, corresponding to 1.4- and | |
| 1.7-fold enhancements in PMA and VCMA, respectively, compared to the case of | |
| room-temperature deposition of CoFeB. The improvement in the MTJ properties was | |
| not simply due to the morphology of the MTJ films. The interface-sensitive | |
| magneto-transport properties indicated that interfacial qualities such as | |
| intermixing and oxidation states at the MgO/CoFeB interfaces were improved by | |
| the cryogenic temperature deposition. Cryogenic-temperature sputtering | |
| deposition is expected to be a standard manufacturing process for | |
| next-generation magnetoresistive random-access memory.",2301.04823v1 | |
| 2007-02-09,X-ray photoemission study of CoFeB/MgO thin film bi-layers,"We present results from an X-ray photoemission spectroscopy (XPS) study of | |
| CoFeB/MgO bi-layers where we observe process-dependent formation of B, Fe, and | |
| Co oxides at the CoFeB/MgO interface due to oxidation of CoFeB during MgO | |
| deposition. Vacuum annealing reduces the Co and Fe oxides but further | |
| incorporates B into the MgO forming a composite MgBxOy layer. Inserting an Mg | |
| layer between CoFeB and MgO introduces an oxygen sink, providing increased | |
| control over B content in the barrier.",0702232v1 | |
| 2005-04-03,Dependence of Giant Tunnel Magnetoresistance of Sputtered CoFeB/MgO/CoFeB Magnetic Tunnel Junctions on MgO Barrier Thickness and Annealing Temperatur,"We investigated the dependence of giant tunnel magnetoresistance (TMR) on the | |
| thickness of an MgO barrier and on the annealing temperature of sputtered | |
| CoFeB/MgO/CoFeB magnetic tunnel junctions deposited on SiO2/Si wafers. The | |
| resistance-area product exponentially increases with MgO thickness, indicating | |
| that the quality of MgO barriers is high in the investigated thickness range of | |
| 1.15-2.4 nm. High-resolution transmission electron microscope images show that | |
| annealing at 375 C results in the formation of crystalline CoFeB/MgO/CoFeB | |
| structures, even though CoFeB electrodes are amorphous in the as-sputtered | |
| state. The TMR ratio increases with annealing temperature and is as high as | |
| 260% at room temperature and 403% at 5 K.",0504051v1 | |
| 2021-03-30,Thermal annealing enhancement of Josephson critical currents in ferromagnetic CoFeB,"The electrical and structural properties of Co40Fe40B20 (CoFeB) alloy are | |
| tunable with thermal annealing. This is key in the optimization of CoFeB-based | |
| spintronic devices, where the advantageously low magnetic coercivity, high spin | |
| polarization, and controllable magnetocrystalline anisotropy are utilised. So | |
| far, there has been no report on superconducting devices based on CoFeB. Here, | |
| we report Nb/CoFeB/Nb Josephson devices and demonstrate an enhancement of the | |
| critical current by up to 700% following thermal annealing due to increased | |
| structural ordering of the CoFeB. The results demonstrate that CoFeB is a | |
| promising material for the development of superconducting spintronic devices.",2103.16136v1 | |
| 2020-06-22,Spin-orbit torque induced magnetisation dynamics and switching in CoFeB/Ta/CoFeB system with mixed magnetic anisotropy,"Spin-orbit torque (SOT) induced magnetisation switching in CoFeB/Ta/CoFeB | |
| trilayer with two CoFeB layers exhibiting in-plane magnetic anisotropy (IPMA) | |
| and perpendicular magnetic anisotropy (PMA) is investigated. Interlayer | |
| exchange coupling (IEC), measured using ferromagnetic resonance technique is | |
| modified by varying thickness of Ta spacer. The evolution of the IEC leads to | |
| different orientation of the magnetic anisotropy axes of two CoFeB layers: for | |
| thicker Ta layer where magnetisation prefers antiferromagnetic ordering and for | |
| thinner Ta layer where ferromagnetic coupling exists. Magnetisation state of | |
| the CoFeB layer exhibiting PMA is controlled by the spin-polarized current | |
| originating from SOT in $\mu m$ sized Hall bars. The evolution of the critical | |
| SOT current density with Ta thickness is presented, showing an increase with | |
| decreasing $t_\mathrm{Ta}$, which coincides with the coercive field dependence. | |
| In a narrow range of $t_\mathrm{Ta}$ corresponding to the ferromagnetic IEC, | |
| the field-free SOT-induced switching is achieved.",2006.12068v1 | |
| 2023-08-17,Interfacial Fe segregation and its influence on magnetic properties of CoFeB/MgFeO multilayers,"We investigated the effect of Fe segregated from partially Fe-substituted MgO | |
| (MgFeO) on the magnetic properties of CoFeB/MgFeO multilayers. X-ray | |
| photoelectron spectroscopy (XPS) as well as magnetic measurements revealed that | |
| the segregated Fe was reduced to metal and exhibited ferromagnetism at the | |
| CoFeB/MgFeO interface. The CoFeB/MgFeO multilayer showed more than 2-fold | |
| enhancement in perpendicular magnetic anisotropy (PMA) energy density compared | |
| with a standard CoFeB/MgO multilayer. The PMA energy density was further | |
| enhanced by inserting an ultrathin MgO layer in between CoFeB and MgFeO layers. | |
| Ferromagnetic resonance measurement also revealed a remarkable reduction of | |
| magnetic damping in the CoFeB/MgFeO multilayers.",2308.08876v1 | |
| 2012-08-29,CoFeB Thickness Dependence of Thermal Stability Factor in CoFeB/MgO Perpendicular Magnetic Tunnel Junctions,"Thermal stability factor (delta) of recording layer was studied in | |
| perpendicular anisotropy CoFeB/MgO magnetic tunnel junctions (p-MTJs) with | |
| various CoFeB recording layer thicknesses and junction sizes. In all series of | |
| p-MTJs with different thicknesses, delta is virtually independent of the | |
| junction sizes of 48-81 nm in diameter. The values of delta increase linearly | |
| with increasing the recording layer thickness. The slope of the linear fit is | |
| explained well by a model based on nucleation type magnetization reversal.",1208.5828v1 | |
| 2016-10-24,Spin orbit effects in CoFeB/MgO hetereostructures with heavy metal underlayers,"We study effects originating from the strong spin orbit coupling in CoFeB/MgO | |
| heterostructures with heavy metal (HM) underlayers. The perpendicular magnetic | |
| anisotropy at the CoFeB/MgO interface, the spin Hall angle of the heavy metal | |
| layer, current induced torques and the Dzyaloshinskii-Moriya interaction at the | |
| HM/CoFeB interfaces are studied for films in which the early 5d transition | |
| metals are used as the HM underlayer. We show how the choice of the HM layer | |
| influences these intricate spin orbit effects that emerge within the bulk and | |
| at interfaces of the heterostructures.",1610.07473v1 | |
| 2014-06-10,Influence of Ta insertions on the magnetic properties of MgO/CoFeB/MgO films probed by ferromagnetic resonance,"We show by vector network analyzer ferromagnetic resonance measurements that | |
| low Gilbert damping {\alpha} down to 0.006 can be achieved in perpendicularly | |
| magnetized MgO/CoFeB/MgO thin films with ultra-thin insertions of Ta in the | |
| CoFeB layer. While increasing the number of Ta insertions allows thicker CoFeB | |
| layers to remain perpendicular, the effective areal magnetic anisotropy does | |
| not improve with more insertions, and also comes with an increase in {\alpha}.",1406.2491v2 | |
| 2017-07-11,Interface Dzyaloshinskii-Moriya interaction in the interlayer exchange antiferromagnetic coupled Pt/CoFeB/Ru/CoFeB systems,"Interfacial Dzyaloshinskii-Moriya interaction (iDMI) in interlayer exchange | |
| coupled (IEC) Pt/Co$_{20}$Fe$_{60}$B$_{20}$(1.12 | |
| nm)/Ru/Co$_{20}$Fe$_{60}$B$_{20}$(1.12 nm) systems have been studied | |
| theoretically and experimentally. Vibrating sample magnetometer has been used | |
| to measure their magnetization at saturation and their interlayer exchange | |
| coupling constants. These latter are found to be of an antiferromagnetic nature | |
| for the investigated Ru range thickness (0.5-1 nm). Their dynamic magnetic | |
| properties were studied using Brillouin light scattering (BLS) technique. The | |
| BLS measurements reveal pronounced non-reciprocal spin waves propagation. In | |
| contrast to the calculations for symmetrical IEC CoFeB layers, this | |
| experimental nonreciprocity is Ru thickness and thus coupling strength | |
| dependent. Therefore, to explain the experimental behaviour, a theoretical | |
| model based on the perpendicular interface anisotropy difference between the | |
| bottom and top CoFeB layers has been developed. We show that the Ru thickness | |
| dependence of the spin wave non-reciprocity is well reproduced by considering a | |
| constant iDMI and different perpendicular interfacial anisotropy fields between | |
| the top and bottom CoFeB layers. This anisotropy difference has been confirmed | |
| by the investigation of the CoFeB thickness dependence of effective | |
| magnetization of Pt/CoFeB/Ru and Ru/CoFeB/MgO individual layers, where a linear | |
| behaviour has been observed.",1707.03427v1 | |
| 2017-09-21,Low Gilbert Damping Constant in Perpendicularly Magnetized W/CoFeB/MgO Films with High Thermal Stability,"Perpendicular magnetic materials with low damping constant and high thermal | |
| stability have great potential for realizing high-density, non-volatile, and | |
| low-power consumption spintronic devices, which can sustain operation | |
| reliability for high processing temperatures. In this work, we study the | |
| Gilbert damping constant ({\alpha}) of perpendicularly magnetized W/CoFeB/MgO | |
| films with a high perpendicular magnetic anisotropy (PMA) and superb thermal | |
| stability. The {\alpha} of these PMA films annealed at different temperatures | |
| is determined via an all-optical Time-Resolved Magneto-Optical Kerr Effect | |
| method. We find that {\alpha} of these W/CoFeB/MgO PMA films decreases with | |
| increasing annealing temperature, reaches a minimum of {\alpha} = 0.016 at an | |
| annealing temperature of 350 {\deg}C, and then increases to 0.024 after | |
| post-annealing at 400 {\deg}C. The minimum {\alpha} observed at 350 {\deg}C is | |
| rationalized by two competing effects as the annealing temperature becomes | |
| higher: the enhanced crystallization of CoFeB and dead-layer growth occurring | |
| at the two interfaces of the CoFeB layer. We further demonstrate that {\alpha} | |
| of the 400 {\deg}C-annealed W/CoFeB/MgO film is comparable to that of a | |
| reference Ta/CoFeB/MgO PMA film annealed at 300 {\deg}C, justifying the | |
| enhanced thermal stability of the W-seeded CoFeB films.",1709.07483v1 | |
| 2018-01-30,"Crystalline structure and XMCD studies of Co40Fe40B20 grown on Bi2Te3, BiTeI and Bi2Se3","Epitaxial films of Co40Fe40B20 (further - CoFeB) were grown on Bi2Te3(001) | |
| and Bi2Se3(001) substrates by laser molecular beam epitaxy (LMBE) technique at | |
| 200-400C. Bcc-type crystalline structure of CoFeB with (111) plane parallel to | |
| (001) plane of Bi2Te3 was observed, in contrast to polycrystalline CoFeB film | |
| formed on Bi2Se3(001) at RT using high-temperature seeding layer. Therefore, | |
| structurally ordered ferromagnetic thin films were obtained on the topological | |
| insulator surface for the first time. Using high energy electron diffraction | |
| (RHEED) 3D reciprocal space mapping, epitaxial relations of main | |
| crystallographic axes for the CoFeB/ Bi2Te3 heterostructure were revealed. MOKE | |
| and AFM measurements showed the isotropic azimuthal in-plane behavior of | |
| magnetization vector in CoFeB/ Bi2Te3, in contrast to 2nd order magnetic | |
| anisotropy seen in CoFeB/Bi2Se3. XPS measurements showed more stable behavior | |
| of CoFeB grown on Bi2Te3 to the oxidation, in compare to CoFeB grown on Bi2Se3. | |
| XAS and XMCD measurements of both concerned nanostructures allowed calculation | |
| of spin and orbital magnetic moments for Co and Fe. Additionally, crystalline | |
| structure and XMCD response of the CoFeB/BiTeI and Co55Fe45/BiTeI systems were | |
| studied, epitaxial relations of main crystallographic axes were found, and spin | |
| and orbital magnetic moments were calculated.",1801.10061v1 | |
| 2005-09-28,Antiferromagnetically coupled CoFeB/Ru/CoFeB trilayers,"This work reports on the magnetic interlayer coupling between two amorphous | |
| CoFeB layers, separated by a thin Ru spacer. We observe an antiferromagnetic | |
| coupling which oscillates as a function of the Ru thickness x, with the second | |
| antiferromagnetic maximum found for x=1.0 to 1.1 nm. We have studied the | |
| switching of a CoFeB/Ru/CoFeB trilayer for a Ru thickness of 1.1 nm and found | |
| that the coercivity depends on the net magnetic moment, i.e. the thickness | |
| difference of the two CoFeB layers. The antiferromagnetic coupling is almost | |
| independent on the annealing temperatures up to 300 degree C while an annealing | |
| at 350 degree C reduces the coupling and increases the coercivity, indicating | |
| the onset of crystallization. Used as a soft electrode in a magnetic tunnel | |
| junction, a high tunneling magnetoresistance of about 50%, a well defined | |
| plateau and a rectangular switching behavior is achieved.",0509749v1 | |
| 2016-12-09,Influence of intermixing at the Ta/CoFeB interface on spin Hall angle in Ta/CoFeB/MgO heterostructures,"We investigate the spin Hall effect in perpendicularly magnetized | |
| Ta/Co40Fe40B20/MgO trilayers with Ta underlayers thicker than the spin | |
| diffusion length. The crystallographic structures of the Ta layer and Ta/CoFeB | |
| interface are examined in detail using X-ray diffraction and transmission | |
| electron microscopy. The thinnest Ta underlayer is amorphous, whereas for | |
| thicker Ta layers a disoriented tetragonal beta-phase appears. Effective | |
| spin-orbit torques are calculated based on harmonic Hall voltage measurements | |
| performed in a temperature range between 15 and 300 K. To account for the | |
| temperature dependence of damping-like and field-like torques, we extend the | |
| spin diffusion model by including an additional contribution from the Ta/CoFeB | |
| interface. Based on this approach, the temperature dependence of the spin Hall | |
| angle in the Ta underlayer and at Ta/CoFeB interface are determined separately. | |
| The results indicate an almost temperature-independent spin Hall angle of | |
| theta_SH-N = -0.2 in Ta and a strongly temperature-dependent theta_SH-I for the | |
| intermixed Ta/CoFeB interface.",1612.03020v1 | |
| 2005-09-28,"Switching of sub-micrometer sized, antiferromagnetically coupled CoFeB/Ru/CoFeB trilayers","This work reports on the magnetic reversal of sub-micrometer sized elements | |
| consisting of an CoFeB/Ru/CoFeB artificial ferrimagnet (AFi). The elements were | |
| patterned into ellipses having a width of approximately 250 to 270nm and a | |
| varying aspect ratio between 1.3 and 8. The coercivity was found to decrease | |
| with an increasing imbalance of the magnetic moment of the two | |
| antiferromagnetically coupled layers and is therefore strongly affected by an | |
| increase of effective anisotropy due to the antiferromagnetic coupling of the | |
| two layers. With respect to a single layer of amorphous CoFeB, patterned in | |
| comparable elements, the AFi has an increased coercivity. Switching asteroids | |
| comparable to single layers were only observed for samples with a high net | |
| moment.",0509750v3 | |
| 2006-02-26,Strong temperature dependence of antiferromagnetic coupling in CoFeB/Ru/CoFeB,"The temperature dependence of saturation and spin-flop fields for artificial | |
| ferrimagnets (AFi) based on antiparallel coupled CoFeB/Ru/CoFeB trilayers has | |
| been investigated in a temperature range between 80K and 600K. The results | |
| presented in this paper are relevant for magnetic devices using this system, | |
| e.g. magnetic-random access memory based on spin-flop switching. In good | |
| accordance to the theory, the saturation field Hsat behaves like Hsat ~ H_0 | |
| (T/T_0)/sinh(T/T_0) with a characteristic temperature of T_0 = 150K. Within | |
| this model, the Fermi velocity for the Ru layer is of the order of 10^5m/s, | |
| therefore, explaining the strong variation of the coupling strength with the | |
| temperature in Ru based AFi. Furthermore, a strong uniaxial anisotropy of K_u = | |
| 2x10^3 J/m^3 with a small angular distribution of the anisotropy axes is | |
| observed for the AFi trilayers based on amorphous CoFeB alloys.",0602609v2 | |
| 2006-06-20,Giant tunnel magnetoresistance and high annealing stability in CoFeB/MgO/CoFeB magnetic tunnel junctions with synthetic pinned layer,"We investigated the relationship between tunnel magnetoresistance (TMR) ratio | |
| and the crystallization of CoFeB layers through annealing in magnetic tunnel | |
| junctions (MTJs) with MgO barriers that had CoFe/Ru/CoFeB synthetic ferrimagnet | |
| pinned layers with varying Ru spacer thickness (tRu). The TMR ratio increased | |
| with increasing annealing temperature (Ta) and tRu, reaching 361% at Ta = 425C, | |
| whereas the TMR ratio of the MTJs with pinned layers without Ru spacers | |
| decreased at Ta over 325C. Ruthenium spacers play an important role in forming | |
| an (001)-oriented bcc CoFeB pinned layer, resulting in a high TMR ratio through | |
| annealing at high temperatures.",0606503v1 | |
| 2013-04-17,Tunneling magneto thermocurrent in CoFeB/MgO/CoFeB based magnetic tunnel junctions,"We study the tunneling magneto thermopower and tunneling magneto | |
| thermocurrent of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJ). The devices | |
| show a clear change of the thermoelectric properties upon reversal of the | |
| magnetisation of the CoFeB layers from parallel to the antiparallel | |
| orientation. When switching from parallel to antiparallel the thermopower | |
| increases by up to 55% where as the thermocurrent drops by 45%. These | |
| observations can be well explained by the Onsager relations taking into account | |
| the tunneling magneto resistance of the MTJ. These findings contrast previous | |
| studies on AlO based MTJ systems, revealing tunneling magneto thermo power but | |
| no tunneling magneto thermocurrent.",1304.4798v1 | |
| 2014-01-18,Enhancement of Perpendicular Magnetic Anisotropy and Transmission of Spin-Hall-Effect-Induced Spin Currents by a Hf Spacer Layer in W/Hf/CoFeB/MgO Layer,"We report that strong perpendicular magnetic anisotropy of the ferromagnetic | |
| layer in a W/CoFeB/MgO multilayer structure can be established by inserting a | |
| Hf layer as thin as 0.25 nm between the W and CoFeB layers. The Hf spacer also | |
| allows transmission of spin currents generated by an in-plane charge current in | |
| the W layer to apply strong spin torque on the CoFeB, thereby enabling | |
| current-driven magnetic switching. The antidamping-like and field-like | |
| components of the spin torque exerted on a 1 nm CoFeB layer are of comparable | |
| magnitudes in this geometry. Both components originate from the spin Hall | |
| effect in the underlying W layer.",1401.4617v1 | |
| 2014-12-12,Asymmetric spin-wave dispersion due to Dzyaloshinskii-Moriya interaction in an ultrathin Pt/CoFeB film,"Employing Brillouin spectroscopy, strong interfacial Dzyaloshinskii-Moriya | |
| interactions have been observed in an ultrathin Pt/CoFeB film. Our | |
| micromagnetic simulations show that spin-wave nonreciprocity due to asymmetric | |
| surface pinning is insignificant for the 0.8nmthick CoFeB film studied. The | |
| observed high asymmetry of the monotonic spin wave dispersion relation is thus | |
| ascribed to strong Dzyaloshinskii-Moriya interactions present at the Pt/CoFeB | |
| interface. Our findings should further enhance the significance of CoFeB as an | |
| important material for magnonic, spintronic and skyrmionic applications.",1412.3907v2 | |
| 2017-04-11,CoFeAlB alloy with low damping and low magnetization for spin transfer torque switching,"We investigate the effect of Al doping on the magnetic properties of the | |
| alloy CoFeB. Comparative measurements of the saturation magnetization, the | |
| Gilbert damping parameter $\alpha$ and the exchange constant as a function of | |
| the annealing temperature for CoFeB and CoFeAlB thin films are presented. Our | |
| results reveal a strong reduction of the magnetization for CoFeAlB in | |
| comparison to CoFeB. If the prepared CoFeAlB films are amorphous, the damping | |
| parameter $\alpha$ is unaffected by the Al doping in comparison to the CoFeB | |
| alloy. In contrast, in the case of a crystalline CoFeAlB film, $\alpha$ is | |
| found to be reduced. Furthermore, the x-ray characterization and the evolution | |
| of the exchange constant with the annealing temperature indicate a similar | |
| crystallization process in both alloys. The data proves the suitability of | |
| CoFeAlB for spin torque switching properties where a reduction of the switching | |
| current in comparison with CoFeB is expected.",1704.03326v1 | |
| 2019-02-20,CoFeB/MgO/CoFeB structures with orthogonal easy axes: perpendicular anisotropy and damping,"We report on the Gilbert damping parameter $\alpha$, the effective | |
| magnetization $4\pi M_{eff}$, and the asymmetry of the $g$-factor in | |
| bottom-CoFeB(0.93~nm)/MgO(0.90--1.25~nm)/CoFeB(1.31~nm)-top as-deposited | |
| systems. | |
| Magnetization of CoFeB layers exhibits a specific noncollinear configuration | |
| with orthogonal easy axes and with $4\pi M_{eff}$ values of $+2.2$ kG and | |
| $-2.3$ kG for the bottom and top layers, respectively. We show that $4\pi | |
| M_{eff}$ depends on the asymmetry $g_\perp - g_\parallel$ of the $g$-factor | |
| measured in the perpendicular and the in-plane directions revealing a highly | |
| nonlinear relationship. In contrast, the Gilbert damping is practically the | |
| same for both layers. Annealing of the films results in collinear easy axes | |
| perpendicular to the plane for both layers. However, the linewidth is strongly | |
| increased due to enhanced inhomogeneous broadening.",1902.07563v1 | |
| 2017-02-17,Spin-orbit torque in MgO/CoFeB/Ta/CoFeB/MgO symmetric structure with interlayer antiferromagnetic coupling,"Spin current generated by spin Hall effect in the heavy metal would diffuse | |
| up and down to adjacent ferromagnetic layers and exert torque on their | |
| magnetization, called spin-orbit torque. Antiferromagnetically coupled | |
| trilayers, namely the so-called synthetic antiferromagnets (SAF), are usually | |
| employed to serve as the pinned layer of spintronic devices based on spin | |
| valves and magnetic tunnel junctions to reduce the stray field and/or increase | |
| the pinning field. Here we investigate the spin-orbit torque in | |
| MgO/CoFeB/Ta/CoFeB/MgO perpendicularly magnetized multilayer with interlayer | |
| antiferromagnetic coupling. It is found that the magnetization of two CoFeB | |
| layers can be switched between two antiparallel states simultaneously. This | |
| observation is replicated by the theoretical calculations by solving | |
| Stoner-Wohlfarth model and Landau-Lifshitz-Gilbert equation. Our findings | |
| combine spin-orbit torque and interlayer coupling, which might advance the | |
| magnetic memories with low stray field and low power consumption.",1702.05331v1 | |
| 2019-09-27,Observation of spin-orbit magnetoresistance in CoFeB/heavy metal/MgO with existence of both spin Hall effect and Edelstein effect,"In this paper, we report the observation of spin-orbit magnetoresistance | |
| (SOMR) in ferromagnetic metal/heavy metal/MgO system. We measure the | |
| magnetoresistance as the function of the thickness of heavy metal (HM) for | |
| CoFeB/HM/MgO and CoFeB/HM films where HM = Pt and Ta. Besides the conventional | |
| spin Hall magnetoresistance (SMR) peak, the evidence of the SOMR is indicated | |
| by another peak of the MR ratio when the thickness of HM is around 1 ~ 2 nm for | |
| CoFeB/HM/MgO films, which is absent for CoFeB/HM films. We speculate the SOMR | |
| observed in our experiment originates from the spin-orbit coupling at the | |
| HM/MgO interface. We give the boundary conditions of our samples and calculate | |
| the theoretical magnetoresistance based on spin diffusion equation. Based on | |
| the theoretical results, we can explain the two peaks we observe separately | |
| comes from the spin current generated by spin Hall effect and by Edelstein | |
| effect.",1909.12811v3 | |
| 2021-08-11,Enhancement of in-plane anisotropy in MoS2/CoFeB bilayers,"Transition metal dichalcogenides (TMD) possess novel properties which makes | |
| them potential candidates for various spintronic applications. Heterostructures | |
| of TMD with magnetic thin film have been extensively considered for | |
| spin-orbital torque, enhancement of perpendicular magnetic anisotropy etc. | |
| However, the effect of TMD on magnetic anisotropy in heterostructures of | |
| in-plane magnetization has not been studied so far. Further the effect of the | |
| TMD on the domain structure and magnetization reversal of the ferromagnetic | |
| system is another important aspect to be understood. In this context we study | |
| the effect of MoS2, a well-studied TMD material, on magnetic properties of | |
| CoFeB in MoS2/CoFeB heterostructures. The reference CoFeB film possess a weak | |
| in-plane anisotropy. However, when the CoFeB is deposited on MoS2 the in-plane | |
| anisotropy is enhanced as observed from magneto optic Kerr effect (MOKE) | |
| microscopy as well as ferromagnetic resonance (FMR). Magnetic domain structure | |
| and magnetization reversal have also been significantly modified for the | |
| MoS2/CoFeB bilayer as compared to the reference CoFeB layer. Frequency and | |
| angle dependent FMR measurement show that the magnetic anisotropy of CoFeB | |
| increases with increase in thickness of MoS2 in the MoS2/CoFeB | |
| heterostructures.",2108.05130v1 | |
| 2023-01-06,Interfacial magnetic anisotropy controlled spin pumping in Co60Fe20B20/Pt stack,"Controlled spin transport in magnetic stacks is required to realize pure spin | |
| current-driven logic and memory devices. The control over the generation and | |
| detection of the pure spin current is achieved by tuning the spin to charge | |
| conversion efficiency of the heavy metal interfacing with ferromagnets. Here, | |
| we demonstrate the direct tunability of spin angular momentum transfer and | |
| thereby spin pumping, in CoFeB/Pt stack, with interfacial magnetic anisotropy. | |
| The ultra-low thickness of CoFeB thin film tilts the magnetic easy axis from | |
| in-plane to out-of-plane due to surface anisotropy. The Ferromagnetic resonance | |
| measurements are performed to investigate the magnetic anisotropy and spin | |
| pumping in CoFeB/Pt stacks. We clearly observe tunable spin pumping effect in | |
| the CoFeB/Pt stacks with varying CoFeB thicknesses. The spin current density, | |
| with varying ferromagnetic layer thickness, is found to increase from 0.11 to | |
| 0.24 MA/m2, with increasing in-plane anisotropy field. Such interfacial | |
| anisotropy-controlled generation of pure spin current can potentially lead to | |
| next-generation anisotropic spin current-controlled spintronic devices.",2301.02370v1 | |
| 2023-06-05,Spin-orbit torque generation in bilayers composed of CoFeB and epitaxial SrIrO$_{3}$ grown on an orthorhombic DyScO$_{3}$ substrate,"We report on the highly efficient spin-orbit torque (SOT) generation in | |
| epitaxial SrIrO$_{3}$(SIO), which is grown on an orthorhombic DyScO$_{3}$(110) | |
| substrate. By conducting harmonic Hall measurement in | |
| Co$_{20}$Fe$_{60}$B$_{20}$ (CoFeB)/SIO bilayers, we characterize two kinds of | |
| the SOTs, i.e., dampinglike (DL) and fieldlike ones to find that the former is | |
| much larger than the latter. By comparison with the Pt control sample with the | |
| same CoFeB thickness, the observed DL SOT efficiency $\xi$$_{DL}$ of SIO | |
| ($\sim$0.32) is three times higher than that of Pt ($\sim$0.093). The | |
| $\xi$$_{DL}$ is nearly constant as a function of the CoFeB thickness, | |
| suggesting that the SIO plays a crucial role in the large SOT generation. These | |
| results on the CoFeB/SIO bilayers highlight that the epitaxial SIO is promising | |
| for low-current and reliable spin-orbit torque-controlled devices.",2306.02567v1 | |
| 2005-09-28,Magnetic properties of antiferromagnetically coupled CoFeB/Ru/CoFeB,"This work reports on the thermal stability of two amorphous CoFeB layers | |
| coupled antiferromagnetically via a thin Ru interlayer. The saturation field of | |
| the artificial ferrimagnet which is determined by the coupling, J, is almost | |
| independent on the annealing temperature up to more than 300 degree C. An | |
| annealing at more than 325 degree C significantly increases the coercivity, Hc, | |
| indicating the onset of crystallization.",0509753v1 | |
| 2008-12-03,Correlation between magnetism and spin-dependent transport in CoFeB alloys,"We report a correlation between the spin polarization of the tunneling | |
| electrons (TSP) and the magnetic moment of amorphous CoFeB alloys. Such a | |
| correlation is surprising since the TSP involves s-like electrons close to the | |
| Fermi level (EF), while the magnetic moment mainly arises due to all | |
| d-electrons below EF. We show that probing the s and d-bands individually | |
| provides clear and crucial evidence for such a correlation to exist through s-d | |
| hybridization, and demonstrate the tuneability of the electronic and magnetic | |
| properties of CoFeB alloys.",0812.0679v1 | |
| 2011-10-03,Spin transfer torque oscillator based on asymmetric magnetic tunnel junctions,"We present a study of the spin transfer torque oscillator based on | |
| CoFeB/MgO/CoFeB asymmetric magnetic tunnel junctions. We observe microwave | |
| precession in junctions with different thickness of the free magnetization | |
| layer. Taking advantage of the ferromagnetic interlayer exchange coupling | |
| between the free and reference layer in the MTJ and perpendicular interface | |
| anisotropy in thin CoFeB electrode we demonstrate the nanometer scale device | |
| that can generate high frequency signal without external magnetic field | |
| applied. The amplitude of the oscillation exceeds 10 nV/Hz^0.5 at 1.5 GHz.",1110.0295v1 | |
| 2014-05-11,Tuning perpendicular magnetic anisotropy in the MgO/CoFeB/Ta thin films,"Understanding the magnetic anisotropy at ferromagnetic metal/oxide interface | |
| is a fundamental and intriguing subject. Here we propose an approach to | |
| manipulate the strength of perpendicular magnetic anisotropy (PMA) by varying | |
| MgO thickness in the MgO/CoFeB/Ta thin films. We identify that the PMA at the | |
| MgO/CoFeB interface is tuned by the crystalline structure of bulk MgO layer and | |
| decreases dramatically due to the onset of crystalline MgO forming with the | |
| increase of MgO thickness. Our work opens an avenue to manipulate the magnetic | |
| anisotropy by the modification of the ferromagnetic metal/oxide interface.",1405.2551v2 | |
| 2017-12-21,Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films,"Spin waves in ferrimagnetic yttrium iron garnet (YIG) films with ultralow | |
| magnetic damping are relevant for magnon-based spintronics and low-power | |
| wave-like computing. The excitation frequency of spin waves in YIG is rather | |
| low in weak external magnetic fields because of its small saturation | |
| magnetization, which limits the potential of YIG films for high-frequency | |
| applications. Here, we demonstrate how exchange-coupling to a CoFeB film | |
| enables efficient excitation of high-frequency perpendicular standing spin | |
| waves (PSSWs) in nanometer-thick (80 nm and 295 nm) YIG films using uniform | |
| microwave magnetic fields. In the 295-nm-thick YIG film, we measure intense | |
| PSSW modes up to 10th order. Strong hybridization between the PSSW modes and | |
| the ferromagnetic resonance mode of CoFeB leads to characteristic anti-crossing | |
| behavior in broadband spin-wave spectra. A dynamic exchange torque at the | |
| YIG/CoFeB interface explains the excitation of PSSWs. The localized torque | |
| originates from exchange coupling between two dissimilar magnetization | |
| precessions in the YIG and CoFeB layers. As a consequence, spin waves are | |
| emitted from the YIG/CoFeB interface and PSSWs form when their wave vector | |
| matches the perpendicular confinement condition. PSSWs are not excited when the | |
| exchange coupling between YIG and CoFeB is suppressed by a Ta spacer layer. | |
| Micromagnetic simulations confirm the exchange-torque mechanism.",1712.08204v1 | |
| 2020-11-14,Observation of multi-skyrmion objects created by size and density control in Ta/CoFeB/MgO films,"Magnetic skyrmions are chiral spin textures with a nontrivial topology that | |
| offer a potential for future magnetic memory and storage devices. The | |
| controlled formation and adjustment of size and density of magnetic skyrmions | |
| in Ta/CoFeB/MgO trilayers is demonstrated. It is the ideal candidate for the | |
| use as a bottom electrode integration into CoFeB/MgO/CoFeB magnetic tunnel | |
| junctions. Varying the CoFeB thickness close to the out-of-plane to in-plane | |
| magnetic phase transition, we find that subtle energy contributions enable the | |
| skyrmion formation in a narrow thickness window, corresponding to only around | |
| 10 pm variation in CoFeB thickness. Using magneto-optical imaging with | |
| quantitative image processing, variations in skyrmion diameter and distribution | |
| below the Abbe limit can be analyzed. We demonstrate a high degree of diameter | |
| and density control. Zero-field stable skyrmions can be set with proper | |
| magnetic field initialization. This demonstrated tunability and degree of | |
| comprehension of skyrmion formation, paves the way for future skyrmion based | |
| magnetic memory. Moreover, we demonstrate a controlled merging of individual | |
| skyrmions to complex topological objects. We compare our results with the | |
| baby-Skyrme model, developed to describe the soliton nature, for any | |
| topological charge n, and demonstrate the ability to form multi-skyrmion | |
| objects. These objects will be interesting for fundamental mathematical studies | |
| of the topological behavior of solitons in the future.",2011.07336v2 | |
| 2020-11-23,Asymmetric depinning of chiral domain walls in ferromagnetic trilayers,"We show that the coupling between two ferromagnetic layers separated by a | |
| nonmagnetic spacer can be used to control the depinning of domain walls and | |
| induce unidirectional domain wall propagation. We investigated CoFeB/Ti/CoFeB | |
| trilayers where the easy axis of the magnetization of the top CoFeB layer is | |
| out-of-plane and that of the bottom layer is in-plane. Using Magneto-optic Kerr | |
| effect microscopy, we find that the depinning of a domain wall in the | |
| perpendicularly magnetized CoFeB layer is influenced by the orientation of the | |
| magnetization of the in-plane layer, which gives rise to a field-driven | |
| asymmetric domain expansion. This effect occurs due to the magnetic coupling | |
| between the internal magnetization of the domain wall and the magnetization of | |
| the in-plane CoFeB layer, which breaks the symmetry of up-down and down-up | |
| homochiral N\'eel domain walls in the perpendicular CoFeB layer. Micromagnetic | |
| simulations support these findings by showing that the interlayer coupling | |
| either opposes or favors the Dzyaloshinskii-Moriya interaction in the domain | |
| wall, thereby generating an imbalance in the depinning fields. This effect also | |
| allows for artificially controlling the chirality and dynamics of domain walls | |
| in magnetic layers lacking a strong Dzyaloshinskii-Moriya interaction.",2011.11290v1 | |
| 2021-02-16,Magnonic band structure in CoFeB/Ta/NiFe meander-shaped magnetic bilayers,"In this work, we investigate the spin-wave propagation in three-dimensional | |
| nanoscale CoFeB/Ta/NiFe meander structures fabricated on a structured SiO2/Si | |
| substrate. The magnonic band structure has been experimentally determined by | |
| wavevector-resolved Brillouin light scattering (BLS) spectroscopy and a set of | |
| stationary modes interposed by two dispersive modes of Bloch type have been | |
| identified. The results could be understood by micromagnetic and finite element | |
| simulations of the mode distributions in both real space and the frequency | |
| domain. The dispersive modes periodically oscillate in frequency over the | |
| Brillouin zones and correspond to modes, whose spatial distributions extend | |
| over the entire sample and are either localized exclusively in the CoFeB layer | |
| or the entire CoFeB/Ta/NiFe magnetic bilayer. Stationary modes are mainly | |
| concentrated in the vertical segments of the CoFeB and NiFe layers and show | |
| negligible amplitudes in the horizon-tal segments. The findings are compared | |
| with those of single-layer CoFeB meander structures with the same geometry | |
| parameters, which reveals the influence of the dipolar coupling between the two | |
| ferromagnetic layers on the magnonic band structure.",2102.08223v2 | |
| 2016-07-20,MegaOhm Extraordinary Hall effect in oxidized CoFeB,"We report on development of controllably oxidized CoFeB ferromagnetic films | |
| demonstrating the extraordinary Hall effect (EHE) resistivity exceeding 1 Ohmcm | |
| and magnetic field sensitivity up to 10^6 Ohm/T. Such EHE resistivity is four | |
| orders of magnitude higher than previously observed in ferromagnetic materials, | |
| while sensitivity is two orders larger than the best of semiconductors",1607.05923v1 | |
| 2016-03-28,Electric-field modulation of exchange stiffness in MgO/CoFeB with perpendicular anisotropy,"We observe magnetic domain structures of MgO/CoFeB with a perpendicular | |
| magnetic easy axis under an electric field. The domain structure shows a maze | |
| pattern with electric-field dependent isotropic period. We find that the | |
| electric-field modulation of the period is explained by considering the | |
| electric-field modulation of the exchange stiffness constant in addition to the | |
| known magnetic anisotropy modulation.",1603.08280v1 | |
| 2006-10-18,Effect of high annealing temperature on giant tunnel magnetoresistance ratio of CoFeB/MgO/CoFeB magnetic tunnel junctions,"We report tunnel magnetoresistance (TMR) ratios as high as 472% at room | |
| temperature and 804% at 5 K in pseudo-spin valve (SV) CoFeB/MgO/CoFeB magnetic | |
| tunnel junctions (MTJs) annealed at 450oC, which is approaching the | |
| theoretically predicted value. By contrast, the TMR ratios for exchange-biased | |
| (EB) SV MTJs with a MnIr antiferromagnetic layer are found to drop when they | |
| are annealed at 450oC. Energy dispersive X-ray analysis shows that annealing at | |
| 450oC induces interdiffusion of Mn and Ru atoms into the MgO barrier and | |
| ferromagnetic layers in EB-SV MTJs. Mechanisms behind the different annealing | |
| behavior are discussed.",0610526v1 | |
| 2011-08-24,Sub-Poissonian shot noise in CoFeB/MgO/CoFeB-based magnetic tunneling junctions,"We measured the shot noise in the CoFeB/MgO/CoFeB-based magnetic tunneling | |
| junctions with a high tunneling magnetoresistance ratio (over 200% at 3 K). | |
| Although the Fano factor in the anti-parallel configuration is close to unity, | |
| it is observed to be typically 0.91\pm0.01 in the parallel configuration. It | |
| indicates the sub-Poissonian process of the electron tunneling in the parallel | |
| configuration due to the relevance of the spin-dependent coherent transport in | |
| the low bias regime.",1108.4831v1 | |
| 2011-09-27,Determination of spin-dependent Seebeck coefficients of CoFeB/MgO/CoFeB magnetic tunnel junction nanopillars,"We investigate the spin-dependent Seebeck coefficient and the tunneling | |
| magneto thermopower of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJ) in the | |
| presence of thermal gradients across the MTJ. Thermal gradients are generated | |
| by an electric heater on top of the nanopillars. The thermo power voltage | |
| across the MTJ is found to scale linearly with the heating power and reveals | |
| similar field dependence as the tunnel magnetoresistance. The amplitude of the | |
| thermal gradient is derived from calibration measurements in combination with | |
| finite element simulations of the heat flux. Based on this, large | |
| spin-dependent Seebeck coefficients of the order of (240 \pm 110) \muV/K are | |
| derived. From additional measurements on MTJs after dielectric breakdown, a | |
| tunneling magneto thermopower up to 90% can be derived for 1.5 nm MgO based MTJ | |
| nanopillars.",1109.5912v1 | |
| 2013-01-09,Low-frequency and shot noises in CoFeB/MgO/CoFeB magnetic tunneling junctions,"The low-frequency and shot noises in spin-valve CoFeB/MgO/CoFeB magnetic | |
| tunneling junctions were studied at low temperature. The measured 1/f noise | |
| around the magnetic hysteresis loops of the free layer indicates that the main | |
| origin of the 1/f noise is the magnetic fluctuation, which is discussed in | |
| terms of a fluctuation-dissipation relation. Random telegraph noise (RTN) is | |
| observed to be symmetrically enhanced in the hysteresis loop with regard to the | |
| two magnetic configurations. We found that this enhancement is caused by the | |
| fluctuation between two magnetic states in the free layer. Although the 1/f | |
| noise is almost independent of the magnetic configuration, the RTN is enhanced | |
| in the antiparallel configuration. These findings indicate the presence of | |
| spin-dependent activation of RTN. Shot noise reveals the spin-dependent | |
| coherent tunneling process via a crystalline MgO barrier.",1301.2161v1 | |
| 2013-05-31,"Effect of Thermal Annealing on Boron Diffusion, Micro-structural, Electrical and Magnetic properties of Laser Ablated CoFeB Thin Films","We report on Boron diffusion and subsequent crystallization of | |
| Co$_{40}$Fe$_{40}$B$_{20}$ (CoFeB) thin films on SiO$_2$/Si(001) substrate | |
| using pulsed laser deposition. Secondary ion mass spectroscopy reveals Boron | |
| diffusion at the interface in both amorphous and crystalline phase of CoFeB. | |
| High-resolution transmission electron microscopy reveals a small fraction of | |
| nano-crystallites embedded in the amorphous matrix of CoFeB. However, annealing | |
| at 400$^\circ$C results in crystallization of CoFe with \textit{bcc} structure | |
| along (110) orientation. As-deposited films are non-metallic in nature with the | |
| coercivity (H$_c$) of 5Oe while the films annealed at 400$^\circ$C are metallic | |
| with a H$_c$ of 135Oe.",1305.7335v1 | |
| 2015-03-02,Exchange bias effect in martensitic epitaxial Ni-Mn-Sn thin films applied to pin CoFeB/MgO/CoFeB magnetic tunnel junctions,"The exchange bias effect is commonly used to shift the coercive field of a | |
| ferromagnet. This technique is crucial for the use of magnetic tunnel junctions | |
| as logic or memory devices. Therefore, an independent switching of the two | |
| ferromagnetic electrodes is necessary to guarantee a reliable readout. Here, we | |
| demonstrate that the intrinsic exchange bias effect of Ni-Mn-Sn can be used to | |
| apply a unidirectional anisotropy to magnetic tunnel junctions. For this, we | |
| use epitaxial Ni-Mn-Sn films as pinning layers for microfabricated | |
| CoFeB/MgO/CoFeB magnetic tunnel junctions. We compare the exchange bias field | |
| ($H_{\text{EB}}$) measured after field cooling in $-10$\,kOe external field by | |
| magnetization measurements with $H_{\text{EB}}$ obtained from tunnel | |
| magnetoresistance measurements. Consistent for both methods we find an exchange | |
| bias of about $H_{\text{EB}}=130$\,Oe at 10\,K, which decreases with increasing | |
| temperature and vanishes above 70\,K.",1503.00440v2 | |
| 2015-03-12,Current induced torques in structures with ultra-thin IrMn antiferromagnet,"Relativistic current induced torques and devices utilizing antiferromagnets | |
| have been independently considered as two promising new directions in | |
| spintronics research. Here we report electrical measurements of the torques in | |
| structures comprising a $\sim1$~nm thick layer of an antiferromagnet IrMn. The | |
| reduced N\'eel temperature and the thickness comparable to the spin-diffusion | |
| length allow us to investigate the role of the antiferromagnetic order in the | |
| ultra-thin IrMn films in the observed torques. In a Ta/IrMn/CoFeB structure, | |
| IrMn in the high-temperature phase diminishes the torque in the CoFeB | |
| ferromagnet. At low temperatures, the antidamping torque in CoFeB flips sign as | |
| compared to the reference Ta/CoFeB structure, suggesting that IrMn in the | |
| antiferromagnetic phase governs the net torque acting on the ferromagnet. At | |
| low temperatures, current induced torque signatures are observed also in a | |
| Ta/IrMn structure comprising no ferromagnetic layer.",1503.03729v2 | |
| 2015-09-14,Thickness-Dependent Magnetoelasticity and its Effects on Perpendicular Magnetic Anisotropy in Ta|CoFeB|MgO Thin Films,"We report measurements of the in-plane magnetoelastic coupling in ultra-thin | |
| Ta|CoFeB|MgO layers as a function of uniaxial strain, conducted using a | |
| four-point bending apparatus. For annealed samples, we observe a strong | |
| dependence on the thickness of the CoFeB layer in the range 1.3-2.0 nm, which | |
| can be modeled as arising from a combination of effective surface and volume | |
| contributions to the magnetoelastic coupling. We point out that if similar | |
| thickness dependence exists for magnetoelastic coupling in response to biaxial | |
| strain, then the standard N\'eel model for the magnetic anisotropy energy | |
| acquires a term inversely proportional to the magnetic layer thickness. This | |
| contribution can significantly change the overall magnetic anisotropy, and | |
| provides a natural explanation for the strongly nonlinear dependence of | |
| magnetic anisotropy energy on magnetic layer thickness that is commonly | |
| observed for ultrathin annealed CoFeB|MgO films with perpendicular magnetic | |
| anisotropy.",1509.04134v1 | |
| 2015-10-20,Evaluation of Spin Waves and Ferromagnetic Resonance Contribution to the Spin Pumping in Ta/CoFeB Structure,"The spin waves and ferromagnetic resonance (FMR) contribution to the spin | |
| pumping signal is studied in the Ta/CoFeB interface under different excitation | |
| bias fields. Ferromagnetic resonance is excited utilizing a coplanar waveguide | |
| and a microwave generator. Using a narrow waveguide of about 3 {\mu}m, | |
| magnetostatic surface spin waves with large wavevector (k) of about 0.81 | |
| {\mu}m^-1 are excited. A large k value results in dissociation of spin waves | |
| and FMR frequencies according to the surface spin wave dispersion relation. | |
| Spin waves and FMR contribution to the spin pumping are calculated based on the | |
| area under the Lorentzian curve fitting over experimental results. It is found | |
| that the FMR over spin waves contribution is about 1 at large bias fields in | |
| Ta/CoFeB structure. Based on our spin pumping results, we propose a method to | |
| characterize the spin wave decay constant which is found to be about 5.5 {\mu}m | |
| in the Ta/CoFeB structure at a bias field of 600 Oe.",1510.05745v1 | |
| 2016-10-08,Perpendicularly magnetized CoFeB multilayers with tunable interlayer exchange for synthetic ferrimagnets,"A study of the multilayer system MgO/CoFeB(1.1nm)/Ta($t$)/CoFeB(0.8nm)/MgO is | |
| presented, where the two CoFeB layers are separated by a Ta interlayer of | |
| varying thickness $t$. The magnetization properties deduced from complementary | |
| techniques such as superconducting quantum interference magnetometry, | |
| ferromagnetic resonance frequency measurements and Brillouin light scattering | |
| spectroscopy can be tuned by changing the Ta thickness between $t$=0.25 nm, 0.5 | |
| nm and 0.75 nm. For $t$=0.5 nm, a ferromagnetic coupling is observed, whereas | |
| for t=0.75 nm, the antiferromagnetic coupling needed to construct a synthetic | |
| ferrimagnet is realized. In the later case, the shape of magnetic domain walls | |
| between two ferrimagnetic alignments or between a ferro- and a ferrimagnetic | |
| alignment is very different. This behavior can be interpreted as a result of | |
| the change in dipolar as well as interlayer exchange energy and domain wall | |
| pinning, which is an important conclusion for the realization of data storage | |
| devices based on synthetic ferri- and antiferromagnets.",1610.02550v1 | |
| 2017-01-05,Excitation and detection of short-waved spin waves in ultrathin Ta/CoFeB/MgO-layer system suitable for spin-orbit-torque magnonics,"We report on the excitation and detection of short-waved spin waves with wave | |
| vectors up to about $40\,\mathrm{rad}\,\mu\mathrm{m}^{-1}$ in spin-wave | |
| waveguides made from ultrathin, in-plane magnetized Co$_{8}$Fe$_{72}$B$_{20}$ | |
| (CoFeB). The CoFeB is incorporated in a layer stack of Ta/CoFeB/Mgo, a layer | |
| system featuring large spin orbit torques and a large perpendicular magnetic | |
| anisotropy constant. The short-waved spin waves are excited by nanometric | |
| coplanar waveguides and are detected via spin rectification and microfocussed | |
| Brillouin light scattering spectroscopy. We show that the large perpendicular | |
| magnetic anisotropy benefits the spin-wave lifetime greatly, resulting in a | |
| lifetime comparable to bulk systems without interfacial damping. The presented | |
| results pave the way for the successful extension of magnonics to ultrathin | |
| asymmetric layer stacks featuring large spin orbit torques.",1701.01399v1 | |
| 2017-01-31,"Lack of correlation between the spin mixing conductance and the ISHE-generated voltages in CoFeB/Pt,Ta bilayers","We investigate spin pumping phenomena in polycrystalline CoFeB/Pt and | |
| CoFeB/Ta bilayers and the correlation between the effective spin mixing | |
| conductance $g^{\uparrow\downarrow}_{\rm eff}$ and the obtained voltages | |
| generated by the spin-to-charge current conversion via the inverse spin Hall | |
| effect in the Pt and Ta layers. For this purpose we measure the in-plane | |
| angular dependence of the generated voltages on the external static magnetic | |
| field and we apply a model to separate the spin pumping signal from the one | |
| generated by the spin rectification effect in the magnetic layer. Our results | |
| reveal a dominating role of anomalous Hall effect for the spin rectification | |
| effect with CoFeB and a lack of correlation between | |
| $g^{\uparrow\downarrow}_{\rm eff}$ and inverse spin Hall voltages pointing to a | |
| strong role of the magnetic proximity effect in Pt in understanding the | |
| observed increased damping. This is additionally reflected on the presence of a | |
| linear dependency of the Gilbert damping parameter on the Pt thickness.",1701.09110v1 | |
| 2017-03-21,Influence of magnetic field and ferromagnetic film thickness on domain pattern transfer in multiferroic heterostructures,"Domains in BaTiO$_3$ induces a regular modulation of uniaxial magnetic | |
| anisotropy in CoFeB via an inverse magnetostriction effect. As a result, the | |
| domain structures of the CoFeB wedge film and BaTiO$_3$ substrate correlate | |
| fully and straight ferroelectric domain boundaries in BaTiO$_3$ pin magnetic | |
| domain walls in CoFeB. We use x-ray photoemission electron microscopy and | |
| magneto-optical Kerr effect microscopy to characterize the spin structure of | |
| the pinned domain walls. In a rotating magnetic field, abrupt and reversible | |
| transitions between two domain wall types occur, namely, narrow walls where the | |
| magnetization vectors align head-to-tail and much broader walls with | |
| alternating head-to-head and tail-to-tail magnetization configurations. We | |
| characterize variations of the domain wall spin structure as a function of | |
| magnetic field strength and CoFeB film thickness and compare the experimental | |
| results with micromagnetic simulations.",1703.07227v1 | |
| 2018-05-31,The current-induced spin-orbit torque and field-free switching from Mo-based magnetic heterostructures,"Magnetic heterostructure Mo/CoFeB/MgO has strong perpendicular magnetic | |
| anisotropy and thermal stability. Through current-induced hysteresis loop shift | |
| measurements, we show that the dampinglike spin-orbit torque (SOT) efficiency | |
| of Mo/CoFeB/MgO heterostructure is $\xi_{DL}\approx -0.003\pm 0.001$ and fairly | |
| independent of the annealing temperature from 300$^\circ$C to 400$^\circ$C. | |
| Though $|\xi_{DL}|$ is small while compare to those from Ta or W-based | |
| heterostructures, reversible current-induced SOT switching of a | |
| thermally-stable Mo/CoFeB/MgO heterostruture can still be achieved. | |
| Furthermore, we observe field-free current-induced switching from a | |
| Mo/CoFeB/MgO structure with the Mo layer being wedge-deposited. Our results | |
| indicate that even for a weak spin-orbit interaction 4d transition metal such | |
| as Mo, it is still possible to generate sufficient spin current for | |
| conventional SOT switching and to realize field-free current-induced switching | |
| by structural engineering.",1805.12322v3 | |
| 2014-06-08,Perpendicular magnetic anisotropy and magnetization process in CoFeB/Pd multilayer films,"Perpendicular magnetic anisotropy (PMA) and dynamic magnetization reversal | |
| process in [CoFeB $t$ nm/Pd 1.0 nm]$_n$ ($t$ = 0.4, 0.6, 0.8, 1.0, and 1.2 nm; | |
| $n$ = 2 - 20) multilayer films have been studied by means of magnetic | |
| hysteresis and Kerr effect measurements. Strong and controllable PMA with an | |
| effective uniaxial anisotropy up to 7.7$\times$ 10$^6$ J.m$^{-3}$ and a | |
| saturation magnetization as low as 200 emu/cc are achieved. Surface/interfacial | |
| anisotropy of CoFeB/Pd interfaces, the main contribution to the PMA, is | |
| separated from the effective uniaxial anisotropy of the films, and appears to | |
| increase with the number of the CoFeB/Pd bilayers. Observation of the magnetic | |
| domains during a magnetization reversal process using polar magneto-optical | |
| Kerr microscopy shows the detailed behavior of nucleation and displacement of | |
| the domain walls.",1406.2028v1 | |
| 2021-01-26,Voltage-controlled antiferromagnetism in magnetic tunnel junctions,"We demonstrate a voltage-controlled exchange bias effect in CoFeB/MgO/CoFeB | |
| magnetic tunnel junctions that is related to the interfacial Fe(Co)Ox formed | |
| between the CoFeB electrodes and the MgO barrier. The unique combination of | |
| interfacial antiferromagnetism, giant tunneling magnetoresistance, and sharp | |
| switching of the perpendicularly-magnetized CoFeB allows sensitive detection of | |
| the exchange bias. It is found that the exchange bias field can be isothermally | |
| controlled by magnetic fields at low temperatures. More importantly, the | |
| exchange bias can also be effectively manipulated by the electric field applied | |
| to the MgO barrier due to the voltage-controlled antiferromagnetic anisotropy | |
| in this system.",2101.11044v1 | |
| 2023-07-27,Interfacial Resonance States-Induced Negative Tunneling Magneto-resistance in Orthogonally-Magnetized CoFeB/MgO/CoFeB,"Magnetic tunneling junctions (MTJs) are essential for non-volatile | |
| magneto-resistive random access memory (MRAM) applications. Here, we report the | |
| observation of a large negative tunneling magneto-resistance (TMR) in the | |
| CoFeB/MgO/CoFeB system with an orthogonally-magnetized configuration. Through | |
| the thickness modulation of the MgO barrier, the negative TMR component can be | |
| enhanced up to 20% under a negative voltage bias. Moreover, the tunnel | |
| anisotropic magneto-resistance measurements unveil that the negative TMR | |
| component likely arises from the interfacial resonance states (IRS) in the | |
| minority band of the bottom ferromagnetic layer. Complementary first principle | |
| calculations further quantify the IRS location and strength with respect to the | |
| Fermi level position. Our work not only confirm the vital role of IRS in the | |
| electrical transport of MTJ, but also provide valuable insights for the design | |
| of new-generation voltage-controlled MRAM and related spintronic applications.",2307.14807v1 | |
| 2024-01-26,Efficient Control of Magnetization Dynamics Via W/CuO$_\text{x}$ Interface,"Magnetization dynamics, which determine the speed of magnetization switching | |
| and spin information propagation, play a central role in modern spintronics. | |
| Gaining its control will satisfy the different needs of various spintronic | |
| devices. In this work, we demonstrate that the surface oxidized Cu | |
| (CuO$_\text{x}$) can be employed for the tunability of magnetization dynamics | |
| of ferromagnet (FM)/heavy metal (HM) bilayer system. The capping CuO$_\text{x}$ | |
| layer in CoFeB/W/CuO$_\text{x}$ trilayer reduces the magnetic damping value in | |
| comparison with the CoFeB/W bilayer. The magnetic damping even becomes lower | |
| than that of the CoFeB/CuO$_\text{x}$ by ~ 16% inferring the stabilization of | |
| anti-damping phenomena. Further, the reduction in damping is accompanied by a | |
| very small reduction in the spin pumping-induced output DC voltage in the | |
| CoFeB/W/CuO$_\text{x}$ trilayer. The simultaneous observation of anti-damping | |
| and spin-to-charge conversion can be attributed to the orbital Rashba effect | |
| observed at the HM/CuO$_\text{x}$ interface. Our experimental findings | |
| illustrate that the cost-effective CuO$_\text{x}$ can be employed as an | |
| integral part of modern spintronics devices owing to its rich underneath | |
| spin-orbital physics.",2401.14708v1 | |
| 2019-04-23,Spin injection and pumping generated by a direct current flowing through a magnetic tunnel junction,"A charge flow through a magnetic tunnel junction (MTJ) leads to the | |
| generation of a spin-polarized current which exerts a spin-transfer torque | |
| (STT) on the magnetization. When the density of applied direct current exceeds | |
| some critical value, the STT excites high-frequency magnetization precession in | |
| the ""free"" electrode of MTJ. Such precession gives rise to microwave output | |
| voltage and, furthermore, can be employed for spin pumping into adjacent normal | |
| metal or semiconductor. Here we describe theoretically the spin dynamics and | |
| charge transport in the CoFeB/MgO/CoFeB/Au tunneling heterostructure connected | |
| to a constant-current source. The magnetization dynamics in the free CoFeB | |
| layer with weak perpendicular anisotropy is calculated by numerical integration | |
| of the Landau-Lifshitz-Gilbert-Slonczewski equation accounting for both STT and | |
| voltage controlled magnetic anisotropy associated with the CoFeB|MgO interface. | |
| It is shown that a large-angle magnetization precession, resulting from | |
| electrically induced dynamic spin reorientation transition, can be generated in | |
| a certain range of relatively low current densities. An oscillating spin | |
| current, which is pumped into the Au overlayer owing to such precession, is | |
| then evaluated together with the injected spin current. Considering both the | |
| driving spin-polarized charge current and the pumped spin current, we also | |
| describe the charge transport in the CoFeB/Au bilayer with the account of | |
| anomalous and inverse spin Hall effects. An electric potential difference | |
| between the lateral sides of the CoFeB/Au bilayer is calculated as a function | |
| of distance from the CoFeB|MgO interface. It is found that this transverse | |
| voltage signal in Au is large enough for experimental detection, which | |
| indicates significant efficiency of the proposed current-driven spin injector.",1904.10361v1 | |
| 2016-05-20,Elementary specific spin and orbital moments of ultrathin CoFeB amorphous films on GaAs(100),"Nanoscale CoFeB amorphous films have been synthesized on GaAs(100) and | |
| studied with X-ray magnetic circular dichroism (XMCD) and transmission electron | |
| microscopy (TEM). We have found that the ratios of the orbital to spin magnetic | |
| moments of both the Co and Fe in the ultrathin amorphous film have been | |
| enhanced by more than 300% compared with those of the bulk crystalline Co and | |
| Fe, and in specifically, a large orbital moment of 0.56*10^-6 B from the Co | |
| atoms has been observed and at the same time the spin moment of the Co atoms | |
| remains comparable to that of the bulk hcp Co. The results indicate that the | |
| large uniaxial magnetic anisotropy (UMA) observed in the ultrathin CoFeB film | |
| on GaAs(100) is related to the enhanced spin-orbital coupling of the Co atoms | |
| in the CoFeB. This work offers experimental evidences of the correlation | |
| between the UMA and the elementary specific spin and orbital moments in the | |
| CoFeB amorphous film on the GaAs(100) substrate, which is significant for | |
| spintronics applications.",1605.06358v1 | |
| 2020-07-24,"Determination of the spin Hall angle, spin mixing conductance and spin diffusion length in Ir/CoFeB for spin-orbitronic devices","Iridium is a very promising material for spintronic applications due to its | |
| interesting magnetic properties such as large RKKY exchange coupling as well as | |
| its large spin-orbit coupling value. Ir is for instance used as a spacer layer | |
| for perpendicular synthetic antiferromagnetic or ferrimagnet systems. However, | |
| only a few studies of the spintronic parameters of this material have been | |
| reported. In this paper, we present inverse spin Hall effect - spin pumping | |
| ferromagnetic resonance measurements on CoFeB/Ir based bilayers to estimate the | |
| values of the effective spin Hall angle, the spin diffusion length within | |
| iridium, and the spin mixing conductance in the CoFeB/Ir bilayer. In order to | |
| have reliable results, we performed the same experiments on CoFeB/Pt bilayers, | |
| which behavior is well known due to numerous reported studies. Our experimental | |
| results show that the spin diffusion length within iridium is 1.3 nm for | |
| resistivity of 250 n$\Omega$.m, the spin mixing conductance $g_{eff}^{\uparrow | |
| \downarrow}$ of the CoFeB/Ir interface is 30 nm$^{-2}$, and the spin Hall angle | |
| of iridium has the same sign than the one of platinum and is evaluated at 26% | |
| of the one of platinum. The value of the spin Hall angle found is 7.7% for Pt | |
| and 2% for Ir. These relevant parameters shall be useful to consider Ir in new | |
| concepts and devices combining spin-orbit torque and spin-transfer torque.",2007.12413v1 | |
| 2010-06-21,Magnonic spin-wave modes in CoFeB antidot lattices,"In this manuscript time-resolved magneto-optical Kerr effect experiments on | |
| structured CoFeB films are presented. The geometries considered are two | |
| dimensional square lattices of micrometer-sized antidots, fabricated by a | |
| focused ion beam. The spin-wave spectra of these magnonic crystals show a novel | |
| precessional mode, which can be related to a Bloch state at the zone boundary. | |
| Additionally, another magnetic mode of different nature appears, whose | |
| frequency displays no dependence on the externally applied magnetic field. | |
| These findings are interpreted as delocalized and localized modes, | |
| respectively.",1006.4038v1 | |
| 2012-02-23,Domain structure in CoFeB thin films with perpendicular magnetic anisotropy,"Domain structures in CoFeB-MgO thin films with a perpendicular easy | |
| magnetization axis were observed by magneto-optic Kerr-effect microscopy at | |
| various temperatures. The domain wall surface energy was obtained by analyzing | |
| the spatial period of the stripe domains and fitting established domain models | |
| to the period. In combination with SQUID measurements of magnetization and | |
| anisotropy energy, this leads to an estimate of the exchange stiffness and | |
| domain wall width in these films. These parameters are essential for | |
| determining whether domain walls will form in patterned structures and devices | |
| made of such materials.",1202.5128v1 | |
| 2012-08-27,Spin-wave modes and band structure of rectangular CoFeB antidot lattices,"We present an investigation of rectangular antidot lattices in a CoFeB film. | |
| Magnonic band structures are numerically calculated, and band gaps are | |
| predicted which shift in frequency by 0.9 GHz when rotating the external field | |
| from the long to the short axis of the unit cell. We demonstrate by | |
| time-resolved experiments that magnonic dipolar surface modes are split in | |
| frequency by 0.6 GHz which agrees well with the theoretical prediction. These | |
| findings provide the basis for directional spin-wave filtering with magnonic | |
| devices.",1208.5339v1 | |
| 2013-07-24,Measurement of magnetization using domain compressibility in CoFeB films with perpendicular anisotropy,"We present a method to map the saturation magnetization of soft ultrathin | |
| films with perpendicular anisotropy, and we illustrate it to assess the | |
| compositional dependence of the magnetization of CoFeB(1 nm)/MgO films. The | |
| method relies on the measurement of the dipolar repulsion of parallel domain | |
| walls that define a linear domain. The film magnetization is linked to the | |
| field compressibility of the domain. The method also yields the minimal | |
| distance between two walls before their merging, which sets a practical limit | |
| to the storage density in spintronic devices using domain walls as storage | |
| entities.",1307.6479v1 | |
| 2016-08-08,Temperature dependence of the spin Hall angle and switching current in the nc-W(O)/CoFeB/MgO system with perpendicular magnetic anisotropy,"We investigated the temperature dependence of the switching current for a | |
| perpendicularly magnetized CoFeB film deposited on a nanocrystalline tungsten | |
| film with large oxygen content: nc-W(O). The spin Hall angle | |
| $|\Theta_\mathrm{SH}| \approx 0.22$ is independent of temperature, whereas the | |
| switching current increases strongly at low temperature. We show that the | |
| nc-W(O) is insensitive to annealing. It thus can be a good choice for the | |
| integration of spin Hall driven writing of information in magnetic memory or | |
| logic devices that require a high-temperature annealing process during | |
| fabrication.",1608.02528v1 | |
| 2017-06-20,Scaling of the Hall effects beyond the quantum resistance threshold in oxidized CoFeB,"The ordinary and the extraordinary Hall effects were studied in gradually | |
| oxidized amorphous CoFeB ferromagnets over six orders of resistivity from the | |
| metallic to the strongly insulating regime. Polarity of the extraordinary Hall | |
| effect reverses, and the amplitude of both the ordinary and the extraordinary | |
| Hall effects increases quadratically with resistivity when resistance exceeds | |
| the quantum resistance threshold. The absolute value of the extraordinary Hall | |
| effect scales linearly with the ordinary one in the entire range over eight | |
| orders of magnitude between the metallic and the insulating states. The | |
| behavior differs qualitatively and quantitatively from theoretically predicted | |
| and experimentally known in other materials.",1706.06392v1 | |
| 2021-01-28,Voltage Controlled Spin-Orbit Torque Switching in W/CoFeB/MgO,"Voltage control of magnetism and spintronics have been highly desirable, but | |
| rarely realized. In this work, we show voltage-controlled spin-orbit torque | |
| (SOT) switching in W/CoFeB/MgO films with perpendicular magnetic anisotropy | |
| (PMA) with voltage administered through SrTiO3 with a high dielectric constant. | |
| We show that a DC voltage can significantly lower PMA by 45%, reduce switching | |
| current by 23%, and increase the damping-like torque as revealed by the first | |
| and second-harmonic measurements. These are characteristics that are | |
| prerequisites for voltage-controlled and voltage-select SOT switching | |
| spintronic devices.",2101.12281v1 | |
| 2023-11-16,Unidirectional propagation of zero-momentum magnons,"We report on experimental observation of unidirectional propagation of | |
| zero-momentum magnons in synthetic antiferromagnet consisting of strained | |
| CoFeB/Ru/CoFeB trilayer. Inherent non-reciprocity of spin waves in synthetic | |
| antiferromagnets with uniaxial anisotropy results in smooth and monotonous | |
| dispersion relation around Gamma point, where the direction of the phase | |
| velocity is reversed, while the group velocity direction is conserved. The | |
| experimental observation of this phenomenon by intensity-, phase-, and | |
| time-resolved Brillouin light scattering microscopy is corroborated by | |
| analytical models and micromagnetic simulations.",2311.10044v1 | |
| 2014-10-14,Low frequency noise peak near magnon emission energy in magnetic tunnel junctions,"We report on the low frequency (LF) noise measurements in magnetic tunnel | |
| junctions (MTJs) below 4 K and at low bias, where the transport is strongly | |
| affected by scattering with magnons emitted by hot tunnelling electrons, as | |
| thermal activation of magnons from the environment is suppressed. For both | |
| CoFeB/MgO/CoFeB and CoFeB/AlO$_{x}$/CoFeB MTJs, enhanced LF noise is observed | |
| at bias voltage around magnon emission energy, forming a peak in the bias | |
| dependence of noise power spectra density, independent of magnetic | |
| configurations. The noise peak is much higher and broader for unannealed | |
| AlO$_{x}$-based MTJ, and besides Lorentzian shape noise spectra in the | |
| frequency domain, random telegraph noise (RTN) is visible in the time traces. | |
| During repeated measurements the noise peak reduces and the RTN becomes | |
| difficult to resolve, suggesting defects being annealed. The Lorentzian shape | |
| noise spectra can be fitted with bias-dependent activation of RTN, with the | |
| attempt frequency in the MHz range, consistent with magnon dynamics. These | |
| findings suggest magnon-assisted activation of defects as the origin of the | |
| enhanced LF noise.",1410.3586v2 | |
| 2015-05-05,Large spin Hall magnetoresistance and its correlation to the spin-orbit torque in W/CoFeB/MgO structures,"The spin-orbit interaction in heavy metal/ferromagnet/oxide structures has | |
| been extensively investigated because it can be employed in manipulation of the | |
| magnetization direction by in-plane current. This implies the existence of an | |
| inverse effect, in which the conductivity in such structures should depend on | |
| the magnetization orientation. In this work, we report a systematic study of | |
| the magnetoresistance (MR) of the W/CoFeB/MgO structures and its correlation to | |
| the current-induced torque to the magnetization. We observe that the MR is | |
| independent of the angle between magnetization and current direction, but is | |
| determined by the relative magnetization orientation with respect to the spin | |
| direction accumulated by spin Hall effect, which is the same symmetry of | |
| so-called spin Hall magnetoresistance. The MR of ~1% in W/CoFeB/MgO samples is | |
| considerably larger than those in other structures of Ta/CoFeB/MgO or | |
| Pt/Co/AlOx, which indicates a larger spin Hall angle of W. Moreover, the | |
| similar W thickness dependence of the MR and the current-induced magnetization | |
| switching efficiency demonstrates that they share the same underlying physics, | |
| which allows one to utilize the MR in non-magnet/ferromagnet structure in order | |
| to understand closely related other spin-orbit coupling effects such as inverse | |
| spin Hall effect, spin-orbit spin transfer torques, etc.",1505.00899v1 | |
| 2020-04-07,Electrical spin injection into InGaAs/GaAs quantum wells: a comparison between MgO tunnel barriers grown by sputtering and molecular beam epitaxy methods,"An efficient electrical spin injection into an InGaAs/GaAs quantum well light | |
| emitting diode is demonstrated thanks to a CoFeB/MgO spin injector. The | |
| textured MgO tunnel barrier is fabricated by two different techniques: | |
| sputtering and molecular beam epitaxy (MBE). The maximal spin injection | |
| efficiency is comparable for both methods. Additionally, the effect of | |
| annealing is also investigated for the two types of samples. Both samples show | |
| the same trend: an increase of the electroluminescence circular polarization | |
| (Pc) with the increase of annealing temperature, followed by a saturation of Pc | |
| beyond 350{\deg}C annealing. Since the increase of Pc starts well below the | |
| crystallization temperature of the full CoFeB bulk layer, this trend could be | |
| mainly due to an improvement of chemical structure at the top CoFeB/MgO | |
| interface. This study reveals that the control of CoFeB/MgO interface is | |
| essential important for an optimal spin injection into semiconductor.",2004.03292v1 | |
| 2020-06-04,Heisenberg Exchange and Dzyaloshinskii-Moriya Interaction in Ultrathin CoFeB Single and Multilayers,"We present results of the analysis of Brillouin Light Scattering (BLS) | |
| measurements of spin waves performed on ultrathin single and multirepeat CoFeB | |
| layers with adjacent heavy metal layers. From a detailed study of the spin-wave | |
| dispersion relation, we independently extract the Heisenberg exchange | |
| interaction (also referred to as symmetric exchange interaction), the | |
| Dzyaloshinskii-Moriya interaction (DMI, also referred to as antisymmetric | |
| exchange interaction), and the anisotropy field. We find a large DMI in CoFeB | |
| thin films adjacent to a Pt layer and nearly vanishing DMI for CoFeB films | |
| adjacent to a W layer. Furthermore, the residual influence of the dipolar | |
| interaction on the dispersion relation and on the evaluation of the Heisenberg | |
| exchange parameter is demonstrated. In addition, an experimental analysis of | |
| the DMI on the spin-wave lifetime is presented. All these parameters play a | |
| crucial role in designing skyrmionic or spin-orbitronic devices.",2006.02690v1 | |
| 2020-06-25,Perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction at an oxide/ferromagnetic metal interface,"We report on the study of both perpendicular magnetic anisotropy (PMA) and | |
| Dzyaloshinskii-Moriya interaction (DMI) at an oxide/ferromagnetic metal (FM) | |
| interface, i.e. BaTiO3 (BTO)/CoFeB. Thanks to the functional properties of the | |
| BTO film and the capability to precisely control its growth, we are able to | |
| distinguish the dominant role of the oxide termination (TiO2 vs BaO), from the | |
| moderate effect of ferroelectric polarization in the BTO film, on the PMA and | |
| DMI at the oxide/FM interface. We find that the interfacial magnetic anisotropy | |
| energy of the BaO-BTO/CoFeB structure is two times larger than that of the | |
| TiO2-BTO/CoFeB, while the DMI of the TiO2-BTO/CoFeB interface is larger. We | |
| explain the observed phenomena by first-principles calculations, which ascribe | |
| them to the different electronic states around the Fermi level at the | |
| oxide/ferromagnetic metal interfaces and the different spin-flip processes. | |
| This study paves the way for further investigation of the PMA and DMI at | |
| various oxide/FM structures and thus their applications in the promising field | |
| of energy-efficient devices.",2006.14268v1 | |
| 2020-09-29,Structural Phase Dependent Giant Interfacial Spin Transparency in W/CoFeB Thin Film Heterostructure,"Pure spin current has transfigured the energy-efficient spintronic devices | |
| and it has the salient characteristic of transport of the spin angular | |
| momentum. Spin pumping is a potent method to generate pure spin current and for | |
| its increased efficiency high effective spin-mixing conductance (Geff) and | |
| interfacial spin transparency (T) are essential. Here, a giant T is reported in | |
| Sub/W(t)/Co20Fe60B20(d)/SiO2(2 nm) heterostructures in \beta-tungsten (\beta-W) | |
| phase by employing all-optical time-resolved magneto-optical Kerr effect | |
| technique. From the variation of Gilbert damping with W and CoFeB thicknesses, | |
| the spin diffusion length of W and spin-mixing conductances are extracted. | |
| Subsequently, T is derived as 0.81 \pm 0.03 for the \beta-W/CoFeB interface. A | |
| sharp variation of Geff and T with W thickness is observed in consonance with | |
| the thickness-dependent structural phase transition and resistivity of W. The | |
| spin memory loss and two-magnon scattering effects are found to have negligible | |
| contributions to damping modulation as opposed to spin pumping effect which is | |
| reconfirmed from the invariance of damping with Cu spacer layer thickness | |
| inserted between W and CoFeB. The observation of giant interfacial spin | |
| transparency and its strong dependence on crystal structures of W will be | |
| important for pure spin current based spin-orbitronic devices.",2009.14143v1 | |
| 2022-06-10,Large anomalous unidirectional magnetoresistance in a single ferromagnetic layer,"Unidirectional magnetoresistance (UMR) in a ferromagnetic bilayer due to the | |
| spin Hall effects (SHEs) provides a facile means of probing in-plane | |
| magnetization to avoid complex magnetic tunnel junctions. However, the UMR | |
| signal is very weak and usually requires a lock-in amplifier for detection even | |
| in the bilayer involving Ta or Pt with a large spin Hall angle (SHA). Here we | |
| report a type of UMR, termed as the anomalous UMR (AUMR), in a single CoFeB | |
| layer without any adjacent SHE layers, where the UMR signal is about 10 times | |
| larger than that in Ta/CoFeB structures and can be detected by using | |
| conventional dc multimeters in the absence of lock-in amplifiers. We further | |
| demonstrate that the extracted AUMR by excluding thermal contributions shows | |
| reversal signs for the CoFeB and NiFe single layers with opposite SHAs, | |
| indicating that the AUMR may originate from the self-generated spin | |
| accumulation interacting with magnetization through the giant | |
| magnetoresistance-like mechanism. These results suggest that the AUMR | |
| contributes UMR signals larger than the interfacial spin Hall UMR in the | |
| CoFeB-involved systems, providing a convenient and reliable approach to detect | |
| in-plane magnetization for the two-terminal spintronic devices.",2206.04851v1 | |
| 2022-06-14,Probing of large interfacial contribution to spin orbit coupling in CoFeB/Ta heterostructure by ultrafast THz emission spectroscopy,"Ultrafast THz radiation generation from ferromagnetic/nonmagnetic bilayer | |
| heterostructure-based spintronic emitters generally exploits the conversion | |
| from spin- to charge-current within the nonmagnetic layer and its interface | |
| with the ferromagnetic layer. Various possible sub-contributions to the | |
| underlying mechanism of inverse spin Hall effect for the THz emission from such | |
| structures, need to be exploited for not only investigating the intricacies at | |
| the fundamental level in the material properties themselves but also for | |
| improving their performance for broadband and high-power THz emission. Here, we | |
| report ultrafast THz emission from CoFeB/Ta bilayer at varying sample | |
| temperatures in a large range to unravel the role of intrinsic and extrinsic | |
| spin to charge conversion processes. In addition to an enhancement in the THz | |
| emission, its temperature dependence shows a THz signal polarity reversal if | |
| the CoFeB/Ta sample is annealed at an elevated temperature. We extract the | |
| behaviour of the spin Hall resistivity, determine the intrinsic spin Hall | |
| conductivity contribution in it and compare those with the standard Fe/Pt | |
| system. Our results clearly demonstrate a giant interfacial contribution to the | |
| overall spin Hall angle arising from the modified interface in the annealed | |
| CoFeB/Ta, where a sign reversal in the corresponding spin Hall angle is | |
| manifested from the THz amplitude variation with the temperature.",2206.06718v2 | |
| 2022-08-31,Perpendicular magnetic anisotropy in as-deposited CoFeB/MgO thin films,"Fabrication of perpendicularly magnetized ferromagnetic films on various | |
| buffer layers, especially on numerous newly discovered spin-orbit torque (SOT) | |
| materials to construct energy-efficient spin-orbitronic devices, is a | |
| long-standing challenge. Even for the widely used CoFeB/MgO structures, | |
| perpendicular magnetic anisotropy (PMA) can only be established on limited | |
| buffer layers through post-annealing above 300 {\deg}C. Here, we report that | |
| the PMA of CoFeB/MgO films can be established reliably on various buffer layers | |
| in the absence of post-annealing. Further results show that precise control of | |
| MgO thickness, which determines oxygen diffusion in the underneath CoFeB layer, | |
| is the key to obtaining the as-deposited PMA. Interestingly, contrary to | |
| previous understanding, post-annealing does not influence the well-established | |
| as-deposited PMA significantly but indeed enhances unsaturated PMA with a thick | |
| MgO layer by modulating oxygen distributions, rather than crystallinity or Co- | |
| and Fe-O bonding. Moreover, our results indicate that oxygen diffusion also | |
| plays a critical role in the PMA degradation at high temperature. These results | |
| provide a practical approach to build spin-orbitronic devices based on various | |
| high-efficient SOT materials.",2208.14913v1 | |
| 2023-11-20,Interplay between moment-dependent and field-driven unidirectional magnetoresistance in CoFeB/InSb/CdTe heterostructures,"Magnetoresistance effects are crucial for understanding the charge/spin | |
| transport as well as propelling the advancement of spintronic applications. | |
| Here we report the coexistence of magnetic moment-dependent (MD) and magnetic | |
| field-driven (FD) unidirectional magnetoresistance (UMR) effects in | |
| CoFeB/InSb/CdTe heterostructures. The strong spin-orbital coupling of InSb and | |
| the matched impedance at the CoFeB/InSb interface warrant a distinct MD-UMR | |
| effect at room temperature, while the interaction between the in-plane magnetic | |
| field and the Rashba effect at the InSb/CdTe interface induces the marked | |
| FD-UMR signal that dominates the high-field region. Moreover, owning to the | |
| different spin transport mechanisms, these two types of nonreciprocal charge | |
| transport show opposite polarities with respect to the magnetic field | |
| direction, which further enable an effective phase modulation of the | |
| angular-dependent magnetoresistance. Besides, the demonstrations of both the | |
| tunable UMR response and two-terminal spin-orbit torque-driven magnetization | |
| switching validate our CoFeB/InSb/CdTe system as a suitable integrated building | |
| block for multifunctional spintronic device design.",2311.11843v1 | |
| 2024-03-05,Orbital torque switching in perpendicularly magnetized materials,"The orbital Hall effect in light materials has attracted considerable | |
| attention for developing novel orbitronic devices. Here we investigate the | |
| orbital torque efficiency and demonstrate the switching of the perpendicularly | |
| magnetized materials through the orbital Hall material (OHM), i.e., Zirconium | |
| (Zr). The orbital torque efficiency of approximately 0.78 is achieved in the Zr | |
| OHM with the perpendicularly magnetized [Co/Pt]3 sample, which significantly | |
| surpasses that of the perpendicularly magnetized CoFeB/Gd/CoFeB sample | |
| (approximately 0.04). Such notable difference is attributed to the different | |
| spin-orbit correlation strength between the [Co/Pt]3 sample and the | |
| CoFeB/Gd/CoFeB sample, which has been confirmed through the theoretical | |
| calculations. Furthermore, the full magnetization switching of the [Co/Pt]3 | |
| sample with a switching current density of approximately 2.6x106 A/cm2 has been | |
| realized through Zr, which even outperforms that of the W spin Hall material. | |
| Our finding provides a guideline to understand orbital torque efficiency and | |
| paves the way to develop energy-efficient orbitronic devices.",2403.03043v1 | |
| 2005-10-20,Dependence of tunnel magnetoresistance in MgO based magnetic tunnel junctions on Ar pressure during MgO sputtering,"We investigated dependence of tunnel magnetoresistance effect in | |
| CoFeB/MgO/CoFeB magnetic tunnel junctions on Ar pressure during MgO-barrier | |
| sputtering. Sputter deposition of MgO-barrier at high Ar pressure of 10 mTorr | |
| resulted in smooth surface and highly (001) oriented MgO. Using this MgO as a | |
| tunnel barrier, tunnel magnetoresistance (TMR) ratio as high as 355% at room | |
| temperature (578% at 5K) was realized after annealing at 325 C or higher, which | |
| appears to be related to a highly (001) oriented CoFeB texture promoted by the | |
| smooth and highly oriented MgO. Electron-beam lithography defined | |
| deep-submicron MTJs having a low-resistivity Au underlayer with the | |
| high-pressure deposited MgO showed high TMR ratio at low resistance-area | |
| product (RA) below 10 ohm-um^2 as 27% at RA = 0.8 ohm-um^2, 77% at RA = 1.1 | |
| ohm-um^2, 130% at RA = 1.7 ohm-um^2, and 165% at RA = 2.9 ohm-um^2.",0510531v1 | |
| 2005-10-20,Current-driven magnetization switching in CoFeB/MgO/CoFeB magnetic tunnel junctions,"Current-driven magnetization switching in low-resistance | |
| Co40Fe40B20/MgO/Co40Fe40B20 magnetic tunnel junctions (MTJs) is reported. The | |
| critical-current densities Jc required for current-driven switching in samples | |
| annealed at 270C and 300C are found to be as low as 7.8 x 10^5 A/cm^2 and 8.8 x | |
| 10^5 A/cm^2 with accompanying tunnel magnetoresistance (TMR) ratios of 49% and | |
| 73 %, respectively. Further annealing of the samples at 350C increases TMR | |
| ratio to 160 %, while accompanying Jc increases to 2.5 x 10^6 A/cm^2. We | |
| attribute the low Jc to the high spin-polarization of tunnel current and small | |
| MsV product of the CoFeB single free layer, where Ms is the saturation | |
| magnetization and V the volume of the free layer.",0510538v1 | |
| 2006-09-13,Current-induced magnetization switching in MgO barrier based magnetic tunnel junctions with CoFeB/Ru/CoFeB synthetic ferrimagnetic free layer,"We report the intrinsic critical current density (Jc0) in current-induced | |
| magnetization switching and the thermal stability factor (E/kBT, where E, kB, | |
| and T are the energy potential, the Boltzmann constant, and temperature, | |
| respectively) in MgO based magnetic tunnel junctions with a | |
| Co40Fe40B20(2nm)/Ru(0.7-2.4nm)/Co40Fe40B20(2nm) synthetic ferrimagnetic (SyF) | |
| free layer. We show that Jc0 and E/kBT can be determined by analyzing the | |
| average critical current density as a function of coercivity using the | |
| Slonczewski's model taking into account thermal fluctuation. We find that high | |
| antiferromagnetic coupling between the two CoFeB layers in a SyF free layer | |
| results in reduced Jc0 without reducing high E/kBT.",0609306v2 | |
| 2009-08-15,Thermal-magnetic noise measurement of spin-torque effects on ferromagnetic resonance in MgO-based magnetic tunnel junctions,"Thermal-magnetic noise at ferromagnetic resonance (T-FMR) can be used to | |
| measure magnetic perpendicular anisotropy of nanoscale magnetic tunnel | |
| junctions (MTJs). For this purpose, T-FMR measurements were conducted with an | |
| external magnetic field up to 14 kOe applied perpendicular to the film surface | |
| of MgO-based MTJs under a dc bias. The observed frequency-field relationship | |
| suggests that a 20 A CoFeB free layer has an effective demagnetization field | |
| much smaller than the intrinsic bulk value of CoFeB, with 4PiMeff = (6.1 +/- | |
| 0.3) kOe. This value is consistent with the saturation field obtained from | |
| magnetometry measurements on extended films of the same CoFeB thickness. | |
| In-plane T-FMR on the other hand shows less consistent results for the | |
| effective demagnetization field, presumably due to excitations of more complex | |
| modes. These experiments suggest that the perpendicular T-FMR is preferred for | |
| quantitative magnetic characterization of nanoscale MTJs.",0908.2164v1 | |
| 2011-04-04,Tunneling magneto thermo power in magnetic tunnel junction nanopillars,"We study the tunneling magneto thermo power (TMTP) in CoFeB/MgO/CoFeB | |
| magnetic tunnel junction nanopillars. Thermal gradients across the junctions | |
| are generated by a micropatterned electric heater line. Thermo power voltages | |
| up to a few tens of \muV between the top and bottom contact of the nanopillars | |
| are measured which scale linearly with the applied heating power and hence with | |
| the applied temperature gradient. The thermo power signal varies by up to 10 | |
| \muV upon reversal of the relative magnetic configuration of the two CoFeB | |
| layers from parallel to antiparallel. This signal change corresponds to a large | |
| spin-dependent Seebeck coefficient of the order of 100 \muV/K and a large TMTP | |
| change of the tunnel junction of up to 90%.",1104.0537v2 | |
| 2012-08-28,Magnetic field sensor with voltage-tunable sensing properties,"We report on a magnetic field sensor based on CoFeB/MgO/CoFeB magnetic tunnel | |
| junctions. By taking advantage of the perpendicular magnetic anisotropy of the | |
| CoFeB/MgO interface, the magnetization of the sensing layer is tilted | |
| out-of-plane which results in a linear response to in-plane magnetic fields. | |
| The application of a bias voltage across the MgO tunnel barrier of the field | |
| sensor affects the magnetic anisotropy and thereby its sensing properties. An | |
| increase of the maximum sensitivity and simultaneous decrease of the magnetic | |
| field operating range by a factor of two is measured. Based on these results, | |
| we propose a voltage-tunable sensor design that allows for active control of | |
| the sensitivity and the operating filed range with the strength and polarity of | |
| the applied bias voltage.",1208.5588v1 | |
| 2013-11-15,Electric-field-induced strain-mediated magnetoelectric effect in CoFeB-MgO magnetic tunnel junctions,"Magnetoelectric coupling between magnetic and electric dipoles is one of the | |
| cornerstones of modern physics towards developing the most energy-efficient | |
| magnetic data storage. Conventionally, magnetoelectric coupling is achieved in | |
| single-phase multiferroics or in magnetoelectric composite nanostructures | |
| consisting of ferromagnetic and ferroelectric/piezoelectric materials. Here, we | |
| demonstrate an electric-field-induced strain-mediated magnetoelectric effect in | |
| ultrathin CoFeB/MgO magnetic tunnel junction employing non-piezoelectric | |
| material, which is a vitally important structure for spintronic devices, by | |
| using dynamical magnetoelectric and piezoresponse force microscopy measurement | |
| techniques. We show that the applied electric-field induces strain in a few | |
| atomic layers of dielectric MgO which is transferred to magnetostrictive CoFeB | |
| layer, resulting in a magnetoelectric effect of magnitude up to 80.8 V cm-1 | |
| Oe-1 under -0.5 V. The demonstrated strain-mediated magnetoelectric effect with | |
| an electric field in magnetic tunnel junctions is a significant step towards | |
| exploring magnetoelectrically controlled spintronic devices for low-power and | |
| high density magnetic data storage applications.",1311.3794v1 | |
| 2014-04-17,Large and robust electrical spin injection into GaAs at zero magnetic field using an ultrathin CoFeB/MgO injector,"We demonstrate a large electrical spin injection into GaAs at zero magnetic | |
| field thanks to an ultrathin perpendicularly magnetized CoFeB contact of a few | |
| atomic planes (1.2 nm). The spin-polarization of electrons injected into GaAs | |
| was examined by the circular polarization of electroluminescence from a Spin | |
| Light Emitting Diode with embedded InGaAs/GaAs quantum wells. The | |
| electroluminescence polarization as a function of the magnetic field closely | |
| traces the out-of-plane magnetization of the CoFeB/MgO injector. A circular | |
| polarization degree of the emitted light as large as 20% at 25 K is achieved at | |
| zero magnetic field. Moreover the electroluminescence circular polarization is | |
| still about 8% at room temperature.",1404.4527v1 | |
| 2014-07-24,Unambiguous separation of the inverse spin Hall and anomalous Nernst Effects within a ferromagnetic metal using the spin Seebeck effect,"The longitudinal spin Seebeck effect is measured on the ferromagnetic | |
| insulator Fe$_3$O$_4$ with the ferromagnetic metal | |
| Co$_{0.2}$Fe$_{0.6}$B$_{0.2}$ (CoFeB) as the spin detector. By using a | |
| non-magnetic spacer material between the two materials (Ti), it is possible to | |
| decouple the two ferromagnetic materials and directly observe pure spin flow | |
| from Fe$_3$O$_4$ into CoFeB. It is shown, that in a single ferromagnetic metal | |
| the inverse spin Hall effect (ISHE) and anomalous Nernst effect (ANE) can occur | |
| simultaneously with opposite polarity. Using this and the large difference in | |
| the coercive fields between the two magnets, it is possible to unambiguously | |
| separate the contributions of the spin Seebeck effect from the ANE and observe | |
| the degree to which each effect contributes to the total response. These | |
| experiments show conclusively that the ISHE and ANE in CoFeB are separate | |
| phenomena with different origins and can coexist in the same material with | |
| opposite response to a thermal gradient.",1407.6758v1 | |
| 2015-05-30,Effect of annealing temperature on exchange stiffness of CoFeB thin films,"We investigate the exchange stiffness constants of 28-nm-thick CoFeB film | |
| using Brillouin light scattering. Series of CoFeB films are prepared on the | |
| MgO(001) substrate with or without additional 5-nm thick MgO buffer layer, the | |
| effect of the annealing temperature on the exchange stiffness constants are | |
| studied. We found that the exchange stiffness constant of 400oC annealed sample | |
| with MgO buffer increased by 10 % form the 200oC annealed sample (=0.73 +/- | |
| 0.01 x 10-11 J/m), while the exchange stiffness constant of without MgO buffer | |
| layer sample increase by 6 % from the as-grown sample (=1.11 +/- 0.02 x 10-11 | |
| J/m).",1506.00129v1 | |
| 2016-02-08,Nanomagnetic logic with non-uniform states of clocking,"Nanomagnetic logic transmits information along a path of nanomagnets. The | |
| basic mechanism to drive such a transmission, known as clocking, can be | |
| achieved by exploiting the spin-Hall effect, as recently observed in | |
| experiments on Ta/CoFeB/MgO multilayers [D. Bhowmik, et al., Nat. Nano. 9, 59 | |
| (2013)]. This paper shows the fundamental mechanism of the spin-Hall driven | |
| clocking by using a full micromagnetic framework and considering two different | |
| devices, Ta/CoFeB/MgO and Pt/CoFeB/MgO. The former is used for a direct | |
| comparison of the numerical results with the experiments while the latter | |
| permits to predict the effect of the Dzyaloshinskii-Moriya interaction (DMI) in | |
| the clocking mechanism. Results show that the clocking state is non-uniform and | |
| it is characterized by the presence of domains separated by Bloch (N\'eel) | |
| domain walls depending on the absence (presence) of the DMI. Our findings point | |
| out that for the design of nanomagnetic logic a full micromagnetic approach is | |
| necessary.",1602.02528v1 | |
| 2016-04-18,Temperature dependence of spin-orbit torques in W/CoFeB bilayers,"We report on the temperature and layer thickness variation of spin-orbit | |
| torques in perpendicularly magnetized W/CoFeB bilayers. Harmonic Hall voltage | |
| measurements reveal dissimilar temperature evolutions of longitudinal and | |
| transverse effective magnetic field components. The transverse effective field | |
| changes sign at 250 K for a 2 nm thick W buffer layer, indicating a much | |
| stronger contribution from interface spin-orbit interactions compared to, for | |
| example, Ta. Transmission electron microscopy measurements reveal that | |
| considerable interface mixing between W and CoFeB is primarily responsible for | |
| this effect.",1604.05204v1 | |
| 2016-04-19,Probing the Dzyaloshinskii-Moriya interaction in CoFeB ultrathin films using domain wall creep and Brillouin light spectroscopy,"We have characterized the strength of the interfacial Dyzaloshinskii-Moriya | |
| interaction (DMI) in ultrathin perpendicularly magnetized CoFeB/MgO films, | |
| grown on different underlayers of W, TaN, and Hf, using two experimental | |
| methods. First, we determined the effective DMI field from measurements of | |
| field-driven domain wall motion in the creep regime, where applied in-plane | |
| magnetic fields induce an anisotropy in the wall propagation that is correlated | |
| with the DMI strength. Second, Brillouin light spectroscopy was employed to | |
| quantify the frequency non-reciprocity of spin waves in the CoFeB layers, which | |
| yielded an independent measurement of the DMI. By combining these results, we | |
| show that DMI estimates from the different techniques only yield qualitative | |
| agreement, which suggests that open questions remain on the underlying models | |
| used to interpret these results.",1604.05475v1 | |
| 2018-01-17,Interference induced enhancement of magneto-optical Kerr effect in ultrathin magnetic films,"We have studied the magneto-optical spectra of ultrathin magnetic films | |
| deposited on Si substrates coated with an oxide layer (SiOx). We find that the | |
| Kerr rotation angle and the ellipticity of ~1 nm thick CoFeB thin films, almost | |
| transparent to visible light, show a strong dependence on the thickness of the | |
| SiOx layer. The Kerr signal from the 1 nm CoFeB thin film can be larger than | |
| that of ~100 nm thick CoFeB films for a given SiOx thickness and light | |
| wavelength. The enhancement of the Kerr signal occurs when optical interference | |
| takes place within the SiOx layer. Interestingly, under such resonance | |
| condition, the measured Kerr signal is in some cases larger than the estimation | |
| despite the good agreement of the measured and calculated reflection amplitude. | |
| We infer the discrepancy originates from interface states that are distinct | |
| from the bulk characteristics. These results show that optical interference | |
| effect can be utilized to study the magneto-optical properties of ultrathin | |
| films.",1801.05539v1 | |
| 2018-03-19,Enhanced spin-orbit torque via interface engineering in Pt/CoFeB/MgO heterostructures,"Spin-orbit torque facilitates efficient magnetization switching via an | |
| in-plane current in perpendicularly magnetized heavy metal/ferromagnet | |
| heterostructures. The efficiency of spin-orbit-torque-induced switching is | |
| determined by the charge-to-spin conversion arising from either bulk or | |
| interfacial spin-orbit interactions, or both. Here, we demonstrate that the | |
| spin-orbit torque and the resultant switching efficiency in Pt/CoFeB systems | |
| are significantly enhanced by an interfacial modification involving Ti | |
| insertion between the Pt and CoFeB layers. Spin pumping and X-ray magnetic | |
| circular dichroism experiments reveal that this enhancement is due to an | |
| additional interface-generated spin current of the nonmagnetic interface and/or | |
| improved spin transparency achieved by suppressing the proximity-induced moment | |
| in the Pt layer. Our results demonstrate that interface engineering affords an | |
| effective approach to improve spin-orbit torque and thereby magnetization | |
| switching efficiency.",1803.06961v1 | |
| 2019-11-28,Spin-torque memristors based on perpendicular magnetic tunnel junctions with a hybrid chiral texture,"Spin-torque memristors were proposed in 2009, which could provide fast, | |
| low-power and infinite memristive behavior for large-density non-volatile | |
| memory and neuromorphic computing. However, the strict requirements of | |
| combining high magnetoresistance, stable intermediate states and spin-polarized | |
| current switching in a single device pose difficulties in physical | |
| implementation. Here, we experimentally demonstrate a nanoscale spin-torque | |
| memristor based on a perpendicular-anisotropy magnetic tunnel junction with a | |
| CoFeB/W/CoFeB composite free layer structure. Its tunneling magnetoresistance | |
| is higher than 200%, and memristive behavior can be realized by spin-transfer | |
| torque switching. Memristive states are maintained by robust domain wall | |
| pinning around clusters of W atoms, where nanoscale vertical chiral spin | |
| textures could be formed through the competition between opposing | |
| Dzyaloshinskii-Moriya interactions and the fluctuating interlayer coupling | |
| caused by the Ruderman-Kittel-Kasuya-Yosida interaction between the two CoFeB | |
| free layers. Spike-timing-dependent plasticity is also demonstrated in this | |
| device.",1911.12784v1 | |
| 2017-05-29,"Contributions of Co and Fe orbitals to Perpendicular Magnetic Anisotropy of MgO/CoFeB Bilayers with Spin-Orbit-Torque-Related (Ta, W, IrMn, and Ti) Underlayers","We study the perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO | |
| bilayers in contact with W, Ta, IrMn and Ti which has been suggested as the | |
| spin-orbit-torque-related underlayers. The saturation magnetization of the | |
| CoFeB depends on the underlayer materials due to formation of a dead-layer, | |
| affecting PMA strength of each film. The x-ray magnetic circular dichroism | |
| measurement reveals that the interfacial intermixing suppresses only the | |
| perpendicular orbital moment of Fe, while the intermixing simultaneously | |
| suppresses both the perpendicular and in-plane orbital moments of Co.",1705.10064v1 | |
| 2019-10-30,Ultra-low switching current density in all-amorphous W-Hf / CoFeB / TaOx films,"We study current-induced deterministic magnetization switching and domain | |
| wall motion via polar Kerr microscopy in all-amorphous | |
| W$_{66}$Hf$_{34}$/CoFeB/TaO$_\text{x}$ with perpendicular magnetic anisotropy | |
| and large spin Hall angle. Investigations of magnetization switching as a | |
| function of in-plane assist field and current pulse-width yield switching | |
| current densities as low as $3\times 10^{9}$ A/m$^2$. We accredit this low | |
| switching current density to a low depinning current density, which was | |
| obtained from measurements of domain wall displacements upon current injection. | |
| This correlation is verified by investigations of a Ta/CoFeB/MgO/Ta reference | |
| sample, which showed critical current densities of at least one order of | |
| magnitude larger, respectively.",1910.13837v3 | |
| 2018-12-05,Voltage-induced strain clocking of nanomagnets with perpendicular magnetic anisotropies,"Nanomagnetic logic (NML) has attracted attention during the last two decades | |
| due to its promise of high energy efficiency combined with non-volatility. Data | |
| transmission in NML relies on Bennett clocking through dipole interaction | |
| between neighboring nanomagnetic bits. This paper uses a fully coupled finite | |
| element model to simulate Bennett clocking based on strain-mediated | |
| multiferroic system for Ni, CoFeB and Terfenol-D with perpendicular magnetic | |
| anisotropies. Simulation results demonstrate that Terfenol-D system has the | |
| highest energy efficiency, which is 2 orders of magnitude more efficient than | |
| Ni and CoFeB. However, the high efficiency is associated with switching | |
| incoherency due to its large magnetostriction coefficient. It is also suggested | |
| that the CoFeB clocking system is slower and has lower bit-density than in Ni | |
| or Terfenol-D systems due to its large dipole coupling. Moreover, we | |
| demonstrate that the precessional perpendicular switching and the Bennett | |
| clocking can be achieved using the same strain-mediated multiferroic | |
| architecture with different voltage pulsing. This study opens new possibilities | |
| to an all-spin in-memory computing system.",1812.02268v1 | |
| 2018-12-18,Enhancement of Spintronic Terahertz Emission via Annealing in Ferromagnetic Heterostructures,"We systematically investigate the influence of annealing effect on terahertz | |
| (THz) generation from CoFeB based magnetic nanofilms driven by femtosecond | |
| laser pulses. Three times enhancement of THz yields are achieved in W/CoFeB | |
| through annealing effect, and double boosting is obtained in Pt/CoFeB. The | |
| mechanism of annealing effect originates from the increase of hot electron mean | |
| free path induced by crystallization, which is experimentally corroborated by | |
| THz transmission measurement on time-domain spectroscopy. Comparison studies of | |
| the thickness dependent THz efficiency after annealing are also implemented, | |
| and we eventually conclude that annealing and thickness optimization are of | |
| importance for scaling up THz intensity. Our observations not only deepen | |
| understanding of the spintronic THz radiation mechanism but also provide normal | |
| platform for high speed spintronic opto-electronic devices.",1812.07113v2 | |
| 2020-04-07,Nonreciprocal Dzyaloshinskii-Moriya magnetoacoustic waves,"We study the interaction of surface acoustic waves with spin waves in | |
| ultra-thin CoFeB/Pt bilayers. Due to the interfacial Dzyaloshinskii-Moriya | |
| interaction (DMI), the spin wave dispersion is non-degenerate for oppositely | |
| propagating spin waves in CoFeB/Pt. In combination with the additional | |
| nonreciprocity of the magnetoacoustic coupling itself, highly nonreciprocal | |
| acoustic wave transmission through the magnetic film is observed. We | |
| systematically characterize the magnetoacoustic wave propagation in a thickness | |
| series of CoFeB($d$)/Pt samples as a function of magnetic field magnitude and | |
| direction, and at frequencies up to 7 GHz. We quantitatively model our results | |
| to extract the strength of the DMI and magnetoacoustic driving fields.",2004.03535v2 | |
| 2021-04-05,"Optical Damage Threshold and THz Generation Efficiency of (Fe,CoFeB)/(Ta,Pt) Spintronic Emitters","THz pulses are generated from femtosecond pulse-excited | |
| ferromagnetic/nonmagnetic spintronic heterostructures via inverse spin Hall | |
| effect. The contribution from ultrafast demagnetization/remagnetization is | |
| extremely weak, in the comparison. The highest possible THz signal strength | |
| from spintronic THz emitters is limited by the optical damage threshold of the | |
| corresponding heterostructures. The THz generation efficiency does not saturate | |
| with the excitation fluence even up till the damage threshold. Bilayer (Fe, | |
| CoFeB)/(Pt, Ta) based FM/NM spintronic heterostructures have been studied for | |
| an optimized performance for THz generation when pumped by sub-50 fs amplified | |
| laser pulses at 800 nm. Among them, CoFeB/Pt is the best combination for an | |
| efficient THz source. The optimized FM/NM spintronic heterostructure on a | |
| quartz substrate, having alpha-phase Ta as the nonmagnetic layer, show the | |
| highest damage threshold as compared to those with Pt, irrespective of their | |
| generation efficiency. The damage threshold of the Fe/Ta heterostructure on | |
| quartz substrate is ~85 GW/cm2.",2104.02028v1 | |
| 2023-02-14,Direct evidence of terahertz emission arising from anomalous Hall effect,"A detailed understanding of the different mechanisms being responsible for | |
| terahertz (THz) emission in ferromagnetic (FM) materials will aid in designing | |
| efficient THz emitters. In this report, we present direct evidence of THz | |
| emission from single layer Co$_{0.4}$Fe$_{0.4}$B$_{0.2}$ (CoFeB) FM thin films. | |
| The dominant mechanism being responsible for the THz emission is the anomalous | |
| Hall effect (AHE), which is an effect of a net backflow current in the FM layer | |
| created by the spin-polarized current reflected at the interfaces of the FM | |
| layer. The THz emission from the AHE-based CoFeB emitter is optimized by | |
| varying its thickness, orientation, and pump fluence of the laser beam. Results | |
| from electrical transport measurements show that skew scattering of charge | |
| carriers is responsible for the THz emission in the CoFeB AHE-based THz | |
| emitter.",2302.07398v2 | |
| 2023-03-21,Inducing or suppressing the anisotropy in multilayers based on CoFeB,"Controlling the uniaxial magnetic anisotropy is of practical interest to a | |
| wide variety of applications. We study Co$_{40}$Fe$_{40}$B$_{20}$ single films | |
| grown on various crystalline orientations of LiNbO$_3$ substrates and on | |
| oxidized silicon. We identify the annealing conditions that are appropriate to | |
| induce or suppress uniaxial anisotropy. Anisotropy fields can be increased by | |
| annealing up to 11 mT when using substrates with anisotropic surfaces. They can | |
| be decreased to below 1 mT when using isotropic surfaces. In the first case, | |
| the observed increase of the anisotropy originates from the biaxial strain in | |
| the film caused by the anisotropic thermal contraction of the substrate when | |
| back at room temperature after strain relaxation during annealing. In the | |
| second case, anisotropy is progressively removed by applying successive | |
| orthogonal fields that are assumed to progressively suppress any chemical | |
| ordering within the magnetic film. The method can be applied to CoFeB/Ru/CoFeB | |
| synthetic antiferromagnets but the tuning of the anisotropy comes with a | |
| decrease of the interlayer exchange coupling and a drastic change of the | |
| exchange stiffness.",2303.11718v1 | |
| 2023-06-19,Spin transport and magnetic proximity effect in CoFeB/normal metal/Pt trilayers,"We present a study of the damping and spin pumping properties of CoFeB/X/Pt | |
| systems with $\rm X=Al,Cr$ and $\rm Ta$. We show that the total damping of the | |
| CoFeB/Pt systems is strongly reduced when an interlayer is introduced | |
| independently of the material. Using a model that considers spin relaxation, we | |
| identify the origin of this contribution in the magnetically polarized Pt | |
| formed by the magnetic proximity effect (MPE), which is suppressed by the | |
| introduction of the interlayer. The induced ferromagnetic order in the Pt layer | |
| is confirmed by transverse magneto-optical Kerr spectroscopy at the M$_{2,3}$ | |
| and N$_7$ absorption edges as an element-sensitive probe. We discuss the impact | |
| of the MPE on parameter extraction in the spin transport model.",2306.11009v2 | |
| 2023-11-09,Magnon-phonon coupling of synthetic antiferromagnets in a surface acoustic wave cavity resonator,"We use a surface acoustic wave (SAW) cavity resonator to study the coupling | |
| of acoustic magnons in a synthetic antiferromagnet (SAF) and the phonons | |
| carried by SAWs. The SAF is composed of a CoFeB/Ru/CoFeB trilayer and the | |
| scattering matrix of the SAW resonator is studied to assess the coupling. We | |
| find that the spectral linewidth of the SAW resonator is modulated when the | |
| frequency of the excited magnons approaches the SAW resonance frequency. | |
| Moreover, the linewidth modulation varies with the magnitude and orientation of | |
| the external magnetic field. Such change in the spectral linewidth can be well | |
| reproduced using macrospin-like model calculations. From the model analyses, we | |
| estimate the magnon-phonon coupling strength to be $\sim$15.6 MHz at a SAW | |
| resonance frequency of 1.8 GHz: the corresponding magnomechanical cooperativity | |
| is $\sim$0.66. As the spectral shape hardly changes in a CoFeB single layer | |
| reference sample under the same experimental condition, these results show that | |
| SAF provides an ideal platform to study magnon-phonon coupling in a SAW cavity | |
| resonator.",2311.05275v1 | |
| 2024-01-15,Multiple Frequency Steps in Synthetic Antiferromagnet Based Double Spin Josephson Junctions Using CoFeB and Fe3Sn,"Superconducting quantum interference device (SQUID) which is made of two | |
| parallel Josephson junctions has applications in magnetometry. A similar | |
| spin-based device is proposed here where spin superfluid in ferromagnet (FM) | |
| mimics the superconducting state. Two materials CoFeB and Fe3Sn are used for | |
| spin superfluid-based SQUID like device where easy plane anisotropy in CoFeB | |
| can be engineered and Fe3Sn has inherent easy plane anisotropy. Frequency | |
| varies in spin based proposed devices. Frequency increases and again decreases | |
| with the increase in both applied magnetic field and applied spin current. The | |
| proposed device can be used as nano oscillator and detector. The frequency in | |
| the proposed device shows multiple frequency steps which can be used for | |
| neuromorphic applications.",2401.08005v1 | |
| 2008-01-09,Current-induced magnetization switching in MgO barrier magnetic tunnel junctions with CoFeB based synthetic ferrimagnetic free layers,"We investigated the effect of using a synthetic ferrimagnetic (SyF) free | |
| layer in MgO-based magnetic tunnel junctions (MTJs) on current-induced | |
| magnetization switching (CIMS), particularly for application to spin-transfer | |
| torque random access memory (SPRAM). The employed SyF free layer had a | |
| Co40Fe40B20/ Ru/ Co40Fe40B20 and Co20Fe60B20/Ru/Co20Fe60B20 structures, and the | |
| MTJs(100x(150-300) nm^2) were annealed at 300oC. The use of SyF free layer | |
| resulted in low intrinsic critical current density (Jc0) without degrading the | |
| thermal-stability factor (E/kBT, where E, kB, and T are the energy potential, | |
| the Boltzmann constant, and temperature,respectively). When the two CoFeB | |
| layers of a strongly antiferromagnetically coupled SyF free layer had the same | |
| thickness, Jc0 was reduced to 2-4x10^6 A/cm^2. This low Jc0 may be due to the | |
| decreased effective volume under the large spin accumulation at the CoFeB/Ru. | |
| The E/kBT was over 60, resulting in a retention time of over ten years and | |
| suppression of the write current dispersion for SPRAM. The use of the SyF free | |
| layer also resulted in a bistable (parallel/antiparallel) magnetization | |
| configuration at zero field, enabling the realization of CIMS without the need | |
| to apply external fields to compensate for the offset field.",0801.1355v1 | |
| 2012-07-11,Layer thickness dependence of the current induced effective field vector in Ta|CoFeB|MgO,"The role of current induced effective magnetic field in ultrathin magnetic | |
| heterostructures is increasingly gaining interest since it can provide | |
| efficient ways of manipulating magnetization electrically. Two effects, known | |
| as the Rashba spin orbit field and the spin Hall spin torque, have been | |
| reported to be responsible for the generation of the effective field. However, | |
| quantitative understanding of the effective field, including its direction with | |
| respect to the current flow, is lacking. Here we show vector measurements of | |
| the current induced effective field in Ta|CoFeB|MgO heterostructrures. The | |
| effective field shows significant dependence on the Ta and CoFeB layers' | |
| thickness. In particular, 1 nm thickness variation of the Ta layer can result | |
| in nearly two orders of magnitude difference in the effective field. Moreover, | |
| its sign changes when the Ta layer thickness is reduced, indicating that there | |
| are two competing effects that contribute to the effective field. The relative | |
| size of the effective field vector components, directed transverse and parallel | |
| to the current flow, varies as the Ta thickness is changed. Our results | |
| illustrate the profound characteristics of just a few atomic layer thick metals | |
| and their influence on magnetization dynamics.",1207.2521v1 | |
| 2013-05-12,Spin Pumping and Inverse Spin Hall Effect in Germanium,"We have measured the inverse spin Hall effect (ISHE) in \textit{n}-Ge at room | |
| temperature. The spin current in germanium was generated by spin pumping from a | |
| CoFeB/MgO magnetic tunnel junction in order to prevent the impedance mismatch | |
| issue. A clear electromotive force was measured in Ge at the ferromagnetic | |
| resonance of CoFeB. The same study was then carried out on several test | |
| samples, in particular we have investigated the influence of the MgO tunnel | |
| barrier and sample annealing on the ISHE signal. First, the reference CoFeB/MgO | |
| bilayer grown on SiO$_{2}$ exhibits a clear electromotive force due to | |
| anisotropic magnetoresistance and anomalous Hall effect which is dominated by | |
| an asymmetric contribution with respect to the resonance field. We also found | |
| that the MgO tunnel barrier is essential to observe ISHE in Ge and that sample | |
| annealing systematically lead to an increase of the signal. We propose a | |
| theoretical model based on the presence of localized states at the interface | |
| between the MgO tunnel barrier and Ge to account for these observations. | |
| Finally, all of our results are fully consistent with the observation of ISHE | |
| in heavily doped $n$-Ge and we could estimate the spin Hall angle at room | |
| temperature to be $\approx$0.001.",1305.2602v1 | |
| 2017-03-10,Room-temperature perpendicular magnetization switching through giant spin-orbit torque from sputtered BixSe(1-x) topological insulator material,"The spin-orbit torque (SOT) arising from materials with large spin-orbit | |
| coupling promises a path for ultra-low power and fast magnetic-based storage | |
| and computational devices. We investigated the SOT from magnetron-sputtered | |
| BixSe(1-x) thin films in BixSe(1-x)/CoFeB heterostructures by using a dc planar | |
| Hall method. Remarkably, the spin Hall angle (SHA) was found to be as large as | |
| 18.83, which is the largest ever reported at room temperature (RT). Moreover, | |
| switching of a perpendicular CoFeB multilayer using SOT from the BixSe(1-x) has | |
| been observed with the lowest-ever switching current density reported in a | |
| bilayer system: 2.3 * 105 A/cm2 at RT. The giant SHA, smooth surface, ease of | |
| growth of the films on silicon substrate, successful growth and switching of a | |
| perpendicular CoFeB multilayer on BixSe(1-x) film opens a path for use of | |
| BixSe(1-x) topological insulator (TI) material as a spin-current generator in | |
| SOT-based memory and logic devices.",1703.03822v1 | |
| 2019-07-08,Bloch-to-Néel domain wall transition evinced through morphology of magnetic bubble expansion in Ta/CoFeB/MgO layers,"Ta/CoFeB/MgO trilayers with perpendicular magnetic anisotropy are often | |
| characterised by vanishing or modest values of interfacial | |
| Dzyaloshinskii-Moriya interaction (DMI), which results in purely Bloch or mixed | |
| Bloch-N\'eel domain walls (DWs). Here we investigate the creep evolution of the | |
| overall magnetic bubble morphology in these systems under the combined presence | |
| of in-plane and out-of-plane magnetic fields and we show that He$^+$ ion | |
| irradiation induces a transition of the internal DW structure towards a fully | |
| N\'eel spin texture. This transition can be correlated to a simultaneous | |
| increase in DMI strength and reduction in saturation magnetisation -- which are | |
| a direct consequence of the effects of ion irradiation on the bottom and top | |
| CoFeB interfaces, respectively. The threshold irradiation dose above which DWs | |
| acquire a pure N\'eel character is experimentally found to be between 12 | |
| $\times$ 10$^{18}$ He$^+$/m$^2$ and 16 $\times$ 10$^{18}$ He$^+$/m$^2$, | |
| matching estimations from the one dimensional DW model based on material | |
| parameters. Our results indicate that evaluating the global bubble shape during | |
| its expansion can be an effective tool to sense the internal bubble DW | |
| structure. Furthermore, we show that ion irradiation can be used to achieve | |
| post-growth engineering of a desired DW spin texture.",1907.03708v1 | |
| 2019-07-14,Current-Induced magnetization switching by the high spin Hall conductivity $α$-W,"The spin Hall effect originating from 5d heavy transition metal thin films | |
| such as Pt, Ta, and W is able to generate efficient spin-orbit torques that can | |
| switch adjacent magnetic layers. This mechanism can serve as an alternative to | |
| conventional spin-transfer torque for controlling next-generation magnetic | |
| memories. Among all 5d transition metals, W in its resistive amorphous phase | |
| typically shows the largest spin-orbit torque efficiency ~ 0.20-0.50. In | |
| contrast, its conductive and crystalline $\alpha$ phase possesses a | |
| significantly smaller efficiency ~ 0.03 and no spin-orbit torque switching has | |
| yet been realized using $\alpha$-W thin films as the spin Hall source. In this | |
| work, through a comprehensive study of high quality W/CoFeB/MgO and the | |
| reversed MgO/CoFeB/W magnetic heterostructures, we show that although | |
| amorphous-W has a greater spin-orbit torque efficiency, the spin Hall | |
| conductivity of $\alpha$-W | |
| ($|\sigma_{\operatorname{SH}}^{\alpha\operatorname{-W}}|=3.71\times10^{5}\operatorname{\Omega}^{-1}\operatorname{m}^{-1}$) | |
| is ~3.5 times larger than that of amorphous-W | |
| ($|\sigma_{\operatorname{SH}}^{\operatorname{amorphous-W}}|=1.05\times10^{5}\operatorname{\Omega}^{-1}\operatorname{m}^{-1}$). | |
| Moreover, we demonstrate spin-orbit torque driven magnetization switching using | |
| a MgO/CoFeB/$\alpha$-W heterostructure. Our findings suggest that the | |
| conductive and high spin Hall conductivity $\alpha$-W can be a potential | |
| candidate for future low power consumption spin-orbit torque memory | |
| applications.",1907.06192v1 | |
| 2019-10-02,A Low Temperature Functioning CoFeB/MgO Based Perpendicular Magnetic Tunnel Junction for Cryogenic Nonvolatile Random Access Memory,"We investigated the low temperature performance of CoFeB/MgO based | |
| perpendicular magnetic tunnel junctions (pMTJs) by characterizing their | |
| quasi-static switching voltage, high speed pulse write error rate and endurance | |
| down to 9 K. pMTJ devices exhibited high magnetoresistance (>120%) and reliable | |
| (error rate<10-4) bi-directional switching with 2 to 200 ns voltage pulses. The | |
| endurance of the devices at 9 K surpassed that at 300 K by three orders of | |
| magnitude under the same write conditions, functioning for more than 10^12 | |
| cycles with 10 ns write pulses. The critical switching voltage at 9 K was | |
| observed to increase by 33% to 93%, depending on pulse duration, compared to | |
| that at 350 K. Ferromagnetic resonance and magnetization measurements on | |
| blanket pMTJ film stacks suggest that the increased switching voltage is | |
| associated with an increase in effective magnetic anisotropy and magnetization | |
| of free layer with decreasing temperature. Our work demonstrates that CoFeB/MgO | |
| based pMTJs have great potential to enable cryogenic MRAM and that their low | |
| temperature magnetization and effective magnetic anisotropy can be further | |
| optimized to lower operating power and improve endurance.",1910.01149v1 | |
| 2018-02-22,Correlation of tunnel magnetoresistance with the magnetic properties in perpendicular CoFeB-based junctions with exchange bias,"We investigate the dependence of magnetic properties on the post-annealing | |
| temperature/time, the thickness of soft ferromagnetic electrode and Ta dusting | |
| layer in the pinned electrode as well as their correlation with the tunnel | |
| magnetoresistance ratio, in a series of perpendicular magnetic tunnel junctions | |
| of materials sequence | |
| Ta/Pd/IrMn/CoFe/Ta$(\textit{x})$/CoFeB/MgO$(\textit{y})$/CoFeB$(\textit{z})$/Ta/Pd. | |
| We obtain a large perpendicular exchange bias of 79.6$\,$kA/m for $x=0.3\,$nm. | |
| For stacks with $z=1.05\,$nm, the magnetic properties of the soft electrode | |
| resemble the characteristics of superparamagnetism. For stacks with | |
| $x=0.4\,$nm, $y=2\,$nm, and $z=1.20\,$nm, the exchange bias presents a | |
| significant decrease at post annealing temperature | |
| $T_\textrm{ann}=330\,^{\circ}$C for 60 min, while the interlayer exchange | |
| coupling and the saturation magnetization per unit area sharply decay at | |
| $T_\textrm{ann}=340\,^{\circ}$C for 60 min. Simultaneously, the tunnel | |
| magnetoresistance ratio shows a peak of $65.5\%$ after being annealed at | |
| $T_\textrm{ann}=300\,^{\circ}$C for 60 min, with a significant reduction down | |
| to $10\%$ for higher annealing temperatures | |
| ($T_\textrm{ann}\geq330\,^{\circ}$C) and down to $14\%$ for longer annealing | |
| times ($T_\textrm{ann}=300\,^{\circ}$C for 90 min). We attribute the large | |
| decrease of tunnel magnetoresistance ratio to the loss of exchange bias in the | |
| pinned electrode.",1802.08002v2 | |
| 2020-04-07,Laser-induced magnetization precession in individual magnetoelastic domains of a multiferroic CoFeB/BaTiO$_3$ composite,"Using a magneto-optical pump-probe technique with micrometer spatial | |
| resolution we show that magnetization precession can be launched in individual | |
| magnetic domains imprinted in a Co$_{40}$Fe$_{40}$B$_{20}$ (CoFeB) layer by | |
| elastic coupling to ferroelectric domains in a BaTiO$_{3}$ substrate. The | |
| dependence of the precession parameters on external magnetic field strength and | |
| orientation reveal that by laser-induced ultrafast partial quenching of the | |
| magnetoelastic coupling parameter of CoFeB by $\approx$27% along with 10% | |
| ultrafast demagnetization trigger the magnetization precession. The relation | |
| between the laser-induced reduction of the magnetoelastic coupling and the | |
| demagnetization is approximated by the $n(n+1)/2$-law with n$\approx$2. This | |
| correspondence confirms the thermal origin of the laser-induced anisotropy | |
| change. Based on the analysis and modeling of the excited precession we find | |
| signatures of laser-induced precessional switching, which occurs when the | |
| magnetic field is applied along the hard magnetization axis and its value is | |
| close to the effective magnetoelastic anisotropy field. The precession | |
| excitation process in an individual magnetoelastic domain is found to be | |
| unaffected by neighboring domains. This makes laser-induced changes of | |
| magnetoelastic anisotropy a promising tool for driving magnetization dynamics | |
| and switching in composite multiferroics with spatial selectivity.",2004.03566v5 | |
| 2018-04-11,Thermographic measurements of spin-current-induced temperature modulation in metallic bilayers,"Spin-to-heat current conversion effects have been investigated in bilayer | |
| films consisting of a paramagnetic metal (PM; Pt, W, or Ta) and a ferromagnetic | |
| metal (FM; CoFeB or permalloy). When a charge current is applied to the PM/FM | |
| bilayer film, a spin current is generated across the PM/FM interface owing to | |
| the spin Hall effect in PM. The spin current was found to exhibit cooling and | |
| heating features depending on the sign of the spin Hall angle of PM, where the | |
| spin-current-induced contribution is estimated by subtracting the contribution | |
| of the anomalous Ettingshausen effect in FM monolayer films. We also found that | |
| the magnitude of the spin-current-induced temperature modulation in the | |
| Pt/CoFeB film is greater than but comparable to that in the Pt/permalloy film, | |
| although the spin dependence of the Peltier coefficient for CoFeB is expected | |
| to be greater than that for permalloy. We discuss the origin of the observed | |
| behaviors with the aid of model calculations; the signals in the PM/FM films | |
| may contain the contributions not only from the electron-driven spin-dependent | |
| Peltier effect but also from the magnon-driven spin Peltier effect.",1804.04068v1 | |
| 2019-09-20,Field-free spin-orbit torque switching through domain wall motion,"Deterministic current-induced spin-orbit torque (SOT) switching of | |
| magnetization in a heavy transition metal/ferromagnetic metal/oxide magnetic | |
| heterostructure with the ferromagnetic layer being perpendicularly-magnetized | |
| typically requires an externally-applied in-plane field to break the switching | |
| symmetry. We show that by inserting an in-plane magnetized ferromagnetic layer | |
| CoFeB underneath the conventional W/CoFeB/MgO SOT heterostructure, | |
| deterministic SOT switching of the perpendicularly-magnetized top CoFeB layer | |
| can be realized without the need of in-plane bias field. Kerr imaging study | |
| further unveils that the observed switching is mainly dominated by domain | |
| nucleation and domain wall motion, which might limit the potentiality of using | |
| this type of multilayer stack design for nanoscale SOT-MRAM application. | |
| Comparison of the experimental switching behavior with micromagnetic | |
| simulations reveals that the deterministic switching in our devices cannot be | |
| explained by the stray field contribution of the in-plane magnetized layer, and | |
| the roughness-caused N\'eel coupling effect might play a more important role in | |
| achieving the observed field-free deterministic switching.",1909.09604v1 | |
| 2019-12-16,Spin-current manipulation of photoinduced magnetization dynamics in heavy metal / ferromagnet double layer based nanostructures,"Spin currents offer a way to control static and dynamic magnetic properties, | |
| and therefore they are crucial for next-generation MRAM devices or spin-torque | |
| oscillators. Manipulating the dynamics is especially interesting within the | |
| context of photo-magnonics. In typical $3d$ transition metal ferromagnets like | |
| CoFeB, the lifetime of light-induced magnetization dynamics is restricted to | |
| about 1 ns, which e.g. strongly limits the opportunities to exploit the wave | |
| nature in a magnonic crystal filtering device. Here, we investigate the | |
| potential of spin-currents to increase the spin wave lifetime in a functional | |
| bilayer system, consisting of a heavy metal (8 nm of $\beta$-Tantalum | |
| (Platinum)) and 5 nm CoFeB. Due to the spin Hall effect, the heavy metal layer | |
| generates a transverse spin current when a lateral charge current passes | |
| through the strip. Using time-resolved all-optical pump-probe spectroscopy, we | |
| investigate how this spin current affects the magnetization dynamics in the | |
| adjacent CoFeB layer. We observed a linear spin current manipulation of the | |
| effective Gilbert damping parameter for the Kittel mode from which we were able | |
| to determine the system's spin Hall angles. Furthermore, we measured a strong | |
| influence of the spin current on a high-frequency mode. We interpret this mode | |
| an an exchange dominated higher order spin-wave resonance. Thus we infer a | |
| strong dependence of the exchange constant on the spin current.",1912.07728v1 | |
| 2019-12-20,Atomistic investigation of the temperature and size dependence of the energy barrier of CoFeB/MgO nanodots,"The balance between low power consumption and high efficiency in memory | |
| devices is a major limiting factor in the development of new technologies. | |
| Magnetic random access memories (MRAM) based on CoFeB/MgO magnetic tunnel | |
| junctions (MTJs) have been proposed as candidates to replace the current | |
| technology due to their non-volatility, high thermal stability and efficient | |
| operational performance. Understanding the size and temperature dependence of | |
| the energy barrier and the nature of the transition mechanism across the | |
| barrier between stable configurations is a key issue in the development of | |
| MRAM. Here we use an atomistic spin model to study the energy barrier to | |
| reversal in CoFeB/MgO nanodots to determine the effects of size, temperature | |
| and external field. We find that for practical device sizes in the 10-50 nm | |
| range the energy barrier has a complex behaviour characteristic of a transition | |
| from a coherent to domain wall driven reversal process. Such a transition | |
| region is not accessible to simple analytical estimates of the energy barrier | |
| preventing a unique theoretical calculation of the thermal stability. The | |
| atomistic simulations of the energy barrier give good agreement with | |
| experimental measurements for similar systems which are at the state of the art | |
| and can provide guidance to experiments identifying suitable materials and MTJ | |
| stacks with the desired thermal stability.",1912.09761v1 | |
| 2020-07-06,Transverse and Longitudinal Spin-Torque Ferromagnetic Resonance for Improved Measurements of Spin-Orbit Torques,"Spin-torque ferromagnetic resonance (ST-FMR) is a common method used to | |
| measure spin-orbit torques (SOTs) in heavy metal/ferromagnet bilayer | |
| structures. In the course of a measurement, other resonant processes such as | |
| spin pumping (SP) and heating can cause spin current or heat flows between the | |
| layers, inducing additional resonant voltage signals via the inverse spin Hall | |
| effect (ISHE) and Nernst effects (NE). In the standard ST-FMR geometry, these | |
| extra artifacts exhibit a dependence on the angle of an in-plane magnetic field | |
| that is identical to the rectification signal from the SOTs. We show | |
| experimentally that the rectification and artifact voltages can be quantified | |
| separately by measuring the ST-FMR signal transverse to the applied current | |
| (i.e., in a Hall geometry) in addition to the usual longitudinal geometry. We | |
| find that in Pt (6 nm)/CoFeB samples the contribution from the artifacts is | |
| small compared to the SOT rectification signal for CoFeB layers thinner than 6 | |
| nm, but can be significant for thicker magnetic layers. We observe a sign | |
| change in the artifact voltage as a function of CoFeB thickness that we suggest | |
| may be due to a competition between a resonant heating effect and the SP/ISHE | |
| contribution.",2007.02850v1 | |
| 2020-12-10,Pulse-width and Temperature Dependence of Memristive Spin-Orbit Torque Switching,"It is crucial that magnetic memory devices formed from magnetic | |
| heterostructures possess sizable spin-orbit torque (SOT) efficiency and high | |
| thermal stability to realize both efficient SOT control and robust storage of | |
| such memory devices. However, most previous studies on various types of | |
| magnetic heterostructures have focused on only their SOT efficiencies, whereas | |
| the thermal stabilities therein have been largely ignored. In this work, we | |
| study the temperature-dependent SOT and stability properties of two types of | |
| W-based heterostructures, namely W/CoFeB/MgO (standard) and CoFeB/W/CoFeB/MgO | |
| (field-free), from 25 ^{\circ}C (298 K) to 80 ^{\circ}C (353 K). Via | |
| temperature-dependent SOT characterization, the SOT efficacies for both systems | |
| are found to be invariant within the range of studied temperatures. | |
| Temperature-dependent current-induced SOT switching measurements further show | |
| that the critical switching current densities decrease with respect to the | |
| ambient temperature; thermal stability factors ({\Delta}) are also found to | |
| degrade as temperature increases for both standard and field-free systems. The | |
| memristive SOT switching behaviors in both systems with various pulse-widths | |
| and temperatures are also examined. Our results suggest that although the SOT | |
| efficacy is robust against thermal effects, the reduction of {\Delta} at | |
| elevated temperatures could be detrimental to standard memory as well as | |
| neuromorphic (memristive) device applications.",2012.05531v1 | |
| 2021-02-06,Spin pumping and inverse spin Hall effect in CoFeB/IrMn heterostructures,"High spin to charge conversion efficiency is the requirement for the | |
| spintronics devices which is governed by spin pumping and inverse spin Hall | |
| effect (ISHE). In last one decade, ISHE and spin pumping are heavily | |
| investigated in ferromagnet/ heavy metal (HM) heterostructures. Recently | |
| antiferromagnetic (AFM) materials are found to be good replacement of HMs | |
| because AFMs exhibit terahertz spin dynamics, high spin-orbit coupling, and | |
| absence of stray field. In this context we have performed the ISHE in CoFeB/ | |
| IrMn heterostructures. Spin pumping study is carried out for | |
| $Co_{40}Fe_{40}B_{20} (12\ nm)/ Cu (3\ nm)/ Ir_{50}Mn_{50} (t\ nm)/ AlO_{x} (3\ | |
| nm)$ samples where \textit{t} value varies from 0 to 10 nm. Damping of all the | |
| samples are higher than the single layer CoFeB which indicates that spin | |
| pumping due to IrMn is the underneath mechanism. Further the spin pumping in | |
| the samples are confirmed by angle dependent ISHE measurements. We have also | |
| disentangled other spin rectifications effects and found that the spin pumping | |
| is dominant in all the samples. From the ISHE analysis the real part of spin | |
| mixing conductance (\textit{$g_{r}^{\uparrow \downarrow}$}) is found to be | |
| 0.704 $\pm$ 0.003 $\times$ $10^{18}$ $m^{-2}$.",2102.03624v2 | |
| 2021-06-10,Spin-Orbit Torque Engineering in β-W/CoFeB Heterostructures via Ta and V Alloying at Interfaces,"Spin-orbit torque manifested as an accumulated spin-polarized moment at | |
| nonmagnetic normal metal, and ferromagnet interfaces is a promising | |
| magnetization switching mechanism for spintronic devices. To fully exploit this | |
| in practice, materials with a high spin Hall angle, i.e., a charge-to-spin | |
| conversion efficiency, are indispensable. To date, very few approaches have | |
| been made to devise new nonmagnetic metal alloys. Moreover, new materials need | |
| to be compatible with semiconductor processing. Here we introduce W-Ta and W-V | |
| alloys and deploy them at the interface between $\beta$-W/CoFeB layers. First, | |
| spin Hall conductivities of W-Ta and W-V structures with various compositions | |
| are carried out by first-principles band calculations, which predict the spin | |
| Hall conductivity of the W-V alloy is improved from $-0.82 \times 10^3$ S/cm | |
| that of W to $-1.98 \times 10^3$ S/cm. Subsequently, heterostructure | |
| fabrication and spin-orbit torque properties are characterized experimentally. | |
| By alloying $\beta$-W with V at a concentration of 20 at%, we observe a large | |
| enhancement of the absolute value of spin Hall conductivity of up to $-(2.77 | |
| \pm 0.31) \times 10^3$ S/cm. By employing X-ray diffraction and scanning | |
| transmission electron microscopy, we further explain the enhancement of | |
| spin-orbit torque efficiency is stemmed from W-V alloy between W and CoFeB.",2106.05460v1 | |
| 2022-11-04,Exchange energies in CoFeB/Ru/CoFeB Synthetic Antiferromagnets,"The interlayer exchange coupling confers specific properties to Synthetic | |
| Antiferromagnets that make them suitable for several applications of | |
| spintronics. The efficient use of this magnetic configuration requires an | |
| in-depth understanding of the magnetic properties and their correlation with | |
| the material structure. Here we establish a reliable procedure to quantify the | |
| interlayer exchange coupling and the intralayer exchange stiffness in synthetic | |
| antiferromagnets; we apply it to the ultrasmooth and amorphous | |
| Co$_{40}$Fe$_{40}$B$_{20}$ (5-40 nm)/Ru/ Co$_{40}$Fe$_{40}$B$_{20}$ material | |
| platform. The complex interplay between the two exchange interactions results | |
| in a gradient of the magnetization orientation across the thickness of the | |
| stack which alters the hysteresis and the spin wave eigenmodes of the stack in | |
| a non trivial way. We measured the field-dependence of the frequencies of the | |
| first four spin waves confined within the thickness of the stack. We modeled | |
| these frequencies and the corresponding thickness profiles of these spin waves | |
| using micromagnetic simulations. The comparison with the experimental results | |
| allows to deduce the magnetic parameters that best account for the sample | |
| behavior. The exchange stiffness is established to be 16 $\pm$ 2 pJ/m, | |
| independently of the Co$_{40}$Fe$_{40}$B$_{20}$ thickness. The interlayer | |
| exchange coupling starts from -1.7 mJ/m$^2$ for the thinnest layers and it can | |
| be maintained above -1.3 mJ/m$^2$ for CoFeB layers as thick as 40 nm. The | |
| comparison of our method with earlier characterizations using the sole | |
| saturation fields argues for a need to revisit the tabulated values of | |
| interlayer exchange coupling in thick synthetic antiferromagnets.",2211.02497v1 | |
| 2023-06-29,Ultrafast THz probing of nonlocal orbital current in transverse multilayer metallic heterostructures,"THz generation from femtosecond photoexcited spintronic heterostructures has | |
| recently become a versatile tool for investigating ultrafast spin-transport and | |
| transient charge-current in a non-contact and non-invasive manner. The same | |
| from the orbital effects is still in the primitive stage. Here, we | |
| experimentally demonstrate orbital-to-charge current conversion in metallic | |
| heterostructures, consisting of a ferromagnetic layer adjacent to either a | |
| light or a heavy metal layer, through detection of the emitted THz pulses. | |
| Temperature-dependent experiments help to disentangle the orbital and spin | |
| components that are manifested in the respective Hall-conductivities, | |
| contributing to THz emission. NiFe/Nb shows the strongest inverse orbital Hall | |
| effect with an experimentally extracted value of effective Hall-conductivity, | |
| \sigma_SOH^int^eff ~ 195 {\Omega}^(-1){cm}^(-1), while CoFeB/Pt shows maximum | |
| contribution from the inverse spin Hall effect. In addition, we observe nearly | |
| ten-fold enhancement in the THz emission due to pronounced orbital-transport in | |
| W-insertion heavy metal layer in CoFeB/W/Ta heterostructure as compared to the | |
| CoFeB/Ta bilayer counterpart.",2306.17027v2 | |
| 2008-06-20,Penetration Depth of Transverse Spin Current in Ferromagnetic Metals,"The line width of the ferromagnetic resonance (FMR) spectrum of | |
| Cu/CoFeB/Cu/Co/Cu is studied. Analyzing the FMR spectrum by the theory of spin | |
| pumping, we determined the penetration depth of the transverse spin current in | |
| the Co layer. The obtained penetration depth of Co is 1.7 nm.",0806.3315v1 | |
| 2019-11-08,Room Temperature Spin to Charge Conversion in Amorphous Topological Insulating Gd-Alloyed BixSe1-x/CoFeB Bilayers,"Disordered topological insulator (TI) films have gained intense interest by | |
| benefiting from both the TIs exotic transport properties and the advantage of | |
| mass production by sputtering. Here, we report on the clear evidence of | |
| spin-charge conversion (SCC) in amorphous Gd-alloyed BixSe1-x (BSG)/CoFeB | |
| bilayers fabricated by sputtering, which could be related to the amorphous TI | |
| surface states. Two methods have been employed to study SCC in BSG/CoFeB(5 nm) | |
| bilayers with different BSG thicknesses. Firstly, spin pumping is used to | |
| generate a spin current in CoFeB and to detect SCC by inverse Edelstein effect. | |
| The maximum SCC efficiency (SCE) is measured as large as 0.035 nm in a 6 nm | |
| thick BSG sample, which shows a strong decay when tBSG increases due to the | |
| increase of BSG surface roughness. The second method is the THz time-domain | |
| spectroscopy, which reveals a small tBSG dependence of SCE, validating the | |
| occurrence of a pure interface state related SCC. Furthermore, our | |
| angle-resolved photoemission spectroscopy data show dispersive two-dimensional | |
| surface states that cross the bulk gap until to the Fermi level, strengthening | |
| the possibility of SCC due to the amorphous TI states. Our studies provide a | |
| new experimental direction towards the search for topological systems in the | |
| amorphous solids.",1911.03323v12 | |
| 2022-08-10,Enhancement of Spin-Charge Conversion Efficiency for Co$_{3}$Sn$_{2}$S$_{2}$ across Transition from Paramagnetic to Ferromagnetic Phase,"Co$_{3}$Sn$_{2}$S$_{2}$ (CSS) is one of the shandite compounds and becomes a | |
| magnetic Weyl semimetal candidate below the ferromagnetic phase transition | |
| temperature ($\textit{T}_\textrm{C}$). In this paper, we investigate the | |
| temperature ($\textit{T}$) dependence of conversion between charge current and | |
| spin current for the CSS thin film by measuring the spin-torque ferromagnetic | |
| resonance (ST-FMR) for the trilayer consisting of CSS / Cu / CoFeB. Above | |
| $\textit{T}_\textrm{C}$ ~ 170 K, the CSS / Cu / CoFeB trilayer exhibits the | |
| clear ST-FMR signal coming from the spin Hall effect in the paramagnetic CSS | |
| and the anisotropic magnetoresistance (AMR) of CoFeB. Below | |
| $\textit{T}_\textrm{C}$, on the other hand, it is found that the ST-FMR signal | |
| involves the dc voltages ($\textit{V}_\textrm{dc}$) not only through the AMR | |
| but also through the giant magnetoresistance (GMR). Thus, the resistance | |
| changes coming from both AMR and GMR should be taken into account to correctly | |
| understand the characteristic field angular dependence of | |
| $\textit{V}_\textrm{dc}$. The spin Hall torque generated from the ferromagnetic | |
| CSS, which possesses the same symmetry as that for spin Hall effect, dominantly | |
| acts on the magnetization of CoFeB. A definite increase in the spin-charge | |
| conversion efficiency ($\xi$) is observed at $\textit{T}$ < | |
| $\textit{T}_\textrm{C}$, indicating that the phase transition to the | |
| ferromagnetic CSS promotes the highly efficient spin-charge conversion. In | |
| addition, our theoretical calculation shows the increase in spin Hall | |
| conductivity with the emergence of magnetic moment at $\textit{T}$ < | |
| $\textit{T}_\textrm{C}$, which is consistent with the experimental observation.",2208.05394v1 | |
| 2023-11-10,Observation by SANS and PNR of pure Néel-type domain wall profiles and skyrmion suppression below room temperature in magnetic [Pt/CoFeB/Ru]$_{10}$ multilayers,"We report investigations of the magnetic textures in periodic [Pt(1 | |
| nm)/(CoFeB(0.8 nm)/Ru(1.4 nm)]$_{10}$ multilayers using polarised neutron | |
| reflectometry (PNR) and small-angle neutron scattering (SANS). The multilayers | |
| are known to host skyrmions stabilized by Dzyaloshinskii-Moriya interactions | |
| induced by broken inversion symmetry and spin-orbit coupling at the asymmetric | |
| interfaces. From depth-dependent PNR measurements, we observe well-defined | |
| structural features, and obtain the layer-resolved magnetization profiles. The | |
| in-plane magnetization of the CoFeB layers calculated from fitting of the PNR | |
| profiles is found to be in excellent agreement with magnetometry data. Using | |
| SANS as a bulk probe of the entire multilayer, we observe long-period magnetic | |
| stripe domains and skyrmion ensembles with full orientational disorder at room | |
| temperature. No sign of skyrmions is found below 250\,K, which we suggest is | |
| due to an increase of a effective magnetic anisotropy in the CoFeB layer on | |
| cooling that suppresses skyrmion stability. Using polarised SANS at room | |
| temperature, we prove the existence of pure N\'eel-type windings in both stripe | |
| domain and skyrmion regimes. No Bloch-type winding admixture, i.e. an | |
| indication for hybrid windings, is detected within the measurement sensitivity, | |
| in good agreement with expectations according to our micromagnetic modelling of | |
| the multilayers. Our findings using neutron techniques offer valuable | |
| microscopic insights into the rich magnetic behavior of skyrmion-hosting | |
| multilayers, which are essential for the advancement of future skyrmion-based | |
| spintronic devices.",2311.05959v2 | |
| 2007-12-17,Spin tunneling in junctions with disordered ferromagnets,"We provide compelling evidence to establish that, contrary to one's | |
| elementary guess, the tunneling spin polarization (TSP) of amorphous CoFeB is | |
| larger than that of highly textured fcc CoFeB. First principles atomic and | |
| electronic structure calculations reveal striking agreement between the | |
| measured TSP and the predicted s-electron spin polarization. Given the | |
| disordered structure of the ternary alloy, not only do these results strongly | |
| endorse our communal understanding of tunneling through AlOx, but they also | |
| portray the key concepts that demand primary consideration in such complex | |
| systems.",0712.2722v1 | |
| 2011-03-22,Inductive determination of the optimum tunnel barrier thickness in magnetic tunnelling junction stacks for spin torque memory applications,"We use pulsed inductive microwave magnetometry to study the precessional | |
| magnetization dynamics of the free layer in CoFeB/MgO/CoFeB based magnetic | |
| tunnelling junction stacks with varying MgO barrier thickness. From the field | |
| dependence of the precession frequency we are able to derive the uniaxial | |
| anisotropy energy and the exchange coupling between the free and the pinned | |
| layer. Furthermore the field dependence of the effective damping parameter is | |
| derived. Below a certain threshold barrier thickness we observe an increased | |
| effective damping for antiparallel orientation of free and pinned layer which | |
| would inhibit reversible low current density spin torque magnetization | |
| reversal. Such inductive measurements, in combination with wafer probe station | |
| based magneto transport experiments, allow a fast determination of the optimum | |
| tunnel barrier thickness range for spin torque memory applications in a | |
| lithography free process.",1103.4248v1 | |
| 2011-06-03,Origin of in-plane uniaxial magnetic anisotropy in CoFeB amorphous ferromagnetic thin-films,"Describing the origin of uniaxial magnetic anisotropy (UMA) is generally | |
| problematic in systems other than single crystals. We demonstrate an in-plane | |
| UMA in amorphous CoFeB films on GaAs(001) which has the expected symmetry of | |
| the interface anisotropy in ferromagnetic films on GaAs(001), but strength | |
| which is independent of, rather than in inverse proportion to, the film | |
| thickness. We show that this volume UMA is consistent with a bond-orientational | |
| anisotropy, which propagates the interface-induced UMA through the thickness of | |
| the amorphous film. It is explained how, in general, this mechanism may | |
| describe the origin of in-plane UMAs in amorphous ferromagnetic films.",1106.0606v1 | |
| 2012-05-13,Voltage-Induced Ferromagnetic Resonance in Magnetic Tunnel Junctions,"We demonstrate excitation of ferromagnetic resonance in CoFeB/MgO/CoFeB | |
| magnetic tunnel junctions (MTJs) by the combined action of voltage-controlled | |
| magnetic anisotropy (VCMA) and spin transfer torque (ST). Our measurements | |
| reveal that GHz-frequency VCMA torque and ST in low-resistance MTJs have | |
| similar magnitudes, and thus that both torques are equally important for | |
| understanding high-frequency voltage-driven magnetization dynamics in MTJs. As | |
| an example, we show that VCMA can increase the sensitivity of an MTJ-based | |
| microwave signal detector to the sensitivity level of semiconductor Schottky | |
| diodes.",1205.2835v2 | |
| 2012-08-08,Spin transfer torque devices utilizing the giant spin Hall effect of tungsten,"We report a giant spin Hall effect (SHE) in {\beta}-W thin films. Using spin | |
| torque induced ferromagnetic resonance with a {\beta}-W/CoFeB bilayer | |
| microstrip we determine the spin Hall angle to be |\theta|=0.30\pm0.02, large | |
| enough for an in-plane current to efficiently reverse the orientation of an | |
| in-plane magnetized CoFeB free layer of a nanoscale magnetic tunnel junction | |
| adjacent to a thin {\beta}-W layer. From switching data obtained with such | |
| 3-terminal devices we independently determine |\theta|=0.33\pm0.06. We also | |
| report variation of the spin Hall switching efficiency with W layers of | |
| different resistivities and hence of variable ({\alpha} and {\beta}) phase | |
| composition.",1208.1711v1 | |
| 2013-03-19,X-ray absorption spectroscopy and magnetic circular dichroism studies of L1_0-Mn-Ga thin films,"Tetragonally distorted \(\rm{Mn}_{3-x}\rm{Ga}_x\) thin films with \(0.1< x < | |
| 2\) show a strong perpendicular magnetic anisotropy and low magnetization and | |
| thus have the potential to serve as electrodes in spin transfer torque magnetic | |
| random access memory. Because a direct capping of these films with MgO is | |
| problematic due to oxide formation, we examined the influence of a CoFeB | |
| interlayer, and of two different deposition methods for the MgO barrier on the | |
| formation of interfacial MnO for \(\rm{Mn}_{62}\rm{Ga}_{38}\) by element | |
| specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism | |
| (XMCD). A highly textured L1\(_0\) crystal structure of the Mn-Ga films was | |
| verified by X-ray diffraction (XRD) measurements. For samples with e-beam | |
| evaporated MgO barrier no evidence for MnO was found, whereas in samples with | |
| magnetron sputtered MgO MnO was detected, even for the thickest interlayer | |
| thickness. Both XAS and XMCD measurements showed an increasing interfacial MnO | |
| amount with decreasing CoFeB interlayer thickness. Additional element specific | |
| full hysteresis loops determined an out-of-plane magnetization axis for the Mn | |
| and Co, respectively.",1303.4648v2 | |
| 2013-05-27,Magnetization reversal in sub-100nm magnetic tunnel junctions with ultrathin MgO barrier biased along hard axis,"We report on room temperature magnetoresistance and low frequency noise in | |
| sub-100nm elliptic CoFeB/MgO/CoFeB magnetic tunnel junctions with ultrathin | |
| (0.9nm) barriers. For magnetic fields applied along the hard axis, we observe | |
| current induced magnetization switching between the antiparallel and parallel | |
| alignments at DC current densities as low as 4*106A/cm2. We attribute the low | |
| value of the critical current to the influence of localized reductions in the | |
| tunnel barrier, which affects the current distribution. The analysis of random | |
| telegraph noise, which appears in the field interval near a magnetization | |
| switch, provides an estimate to the dimension of the pseudo pinholes that | |
| trigger the magnetization switching via local spin torque. Micromagnetic | |
| simulations qualitatively and quantitatively reproduce the main experimental | |
| observations.",1305.6209v1 | |
| 2013-05-29,Enhanced interface perpendicular magnetic anisotropy in Ta|CoFeB|MgO using nitrogen doped Ta underlayers,"We show that the magnetic characteristics of Ta|CoFeB|MgO magnetic | |
| heterostructures are strongly influenced by doping the Ta underlayer with | |
| nitrogen. In particular, the saturation magnetization drops upon doping the Ta | |
| underlayer, suggesting that the doped underlayer acts as a boron diffusion | |
| barrier. In addition, the thickness of the magnetic dead layer decreases with | |
| increasing nitrogen doping. Surprisingly, the interface magnetic anisotropy | |
| increases to ~1.8 erg/cm2 when an optimum amount of nitrogen is introduced into | |
| the Ta underlayer. These results show that nitrogen doped Ta serves as a good | |
| underlayer for Spintronics applications including magnetic tunnel junctions and | |
| domain wall devices.",1305.6660v1 | |
| 2013-08-08,Interface control of the magnetic chirality in TaN|CoFeB|MgO heterosctructures,"Recent advances in the understanding of spin orbital effects in ultrathin | |
| magnetic heterostructures have opened new paradigms to control magnetic moments | |
| electrically. The Dzyaloshinskii-Moriya interaction (DMI) is said to play a key | |
| role in forming a Neel-type domain wall that can be driven by the spin Hall | |
| torque, a torque resulting from the spin current generated in a neighboring | |
| non-magnetic layer via the spin Hall effect. Here we show that the sign of the | |
| DMI, which determines the direction to which a domain wall moves with current, | |
| can be changed by modifying the adjacent non-magnetic layer. We find that the | |
| sense of rotation of a domain wall spiral is reversed when the Ta underlayer is | |
| doped with nitrogen in Ta|CoFeB|MgO heterostructures. The spin Hall angle of | |
| the Ta and nitrogen doped Ta underlayers carry the same sign, suggesting that | |
| the sign of the DMI is defined at the interface. Depending on the sense of | |
| rotation, spin transfer torque and spin Hall torque can either compete or | |
| assist each other, thus influencing the efficiency of moving domain walls with | |
| current.",1308.1751v1 | |
| 2013-10-18,Quantitative characterization of the spin orbit torque using harmonic Hall voltage measurements,"Solid understanding of current induced torques is key to the development of | |
| current and voltage controlled magnetization dynamics in ultrathin magnetic | |
| heterostructures. To evaluate the size and direction of such torques, or | |
| effective fields, a number of methods have been employed. Here we examine the | |
| adiabatic (low frequency) harmonic Hall voltage measurement that has been used | |
| to study the effective field. We derive an analytical formula for the harmonic | |
| Hall voltages to evaluate the effective field for both out of plane and | |
| in-plane magnetized systems. The formula agrees with numerical calculations | |
| based on a macrospin model. Two different in-plane magnetized films, | |
| Pt|CoFeB|MgO and CuIr|CoFeB|MgO are studied using the formula developed. The | |
| effective field obtained for the latter system shows relatively good agreement | |
| with that estimated using a spin torque switching phase diagram measurements | |
| reported previously. Our results illustrate the versatile applicability of | |
| harmonic Hall voltage measurement for studying current induced torques in | |
| magnetic heterostructures.",1310.4879v1 | |
| 2013-12-03,Depth dependent magnetization profiles of hybrid exchange springs,"We report on the magnetization depth profile of a hybrid exchange spring | |
| system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to | |
| a CoFeB thin film with in-plane anisotropy. The competition between these two | |
| orthogonal anisotropies promotes a strong depth dependence of the magnetization | |
| orientation. The angle of the magnetization vector is sensitive both to the | |
| strength of the individual anisotropies and to the local exchange constant, and | |
| is thus tunable by changing the thickness of the CoFeB layer and by | |
| substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic | |
| depth profiles are directly probed by element specific x-ray magnetic circular | |
| dichroism (XMCD) of the Co, Fe, and Ni layers located at different average | |
| depths. The experimental results are corroborated by micromagnetic simulations.",1312.0878v1 | |
| 2014-04-04,Angular and temperature dependence of current induced spin-orbit effective fields in Ta/CoFeB/MgO nanowires,"Current induced spin-orbit effective magnetic fields in | |
| metal/ferromagnet/oxide trilayers provide a new way to manipulate the | |
| magnetization, which is an alternative to the conventional current induced spin | |
| transfer torque arising from noncollinear magnetization. Ta/CoFeB/MgO | |
| structures are expected to be useful for non-volatile memories and logic | |
| devices due to its perpendicular anisotropy and large current induced | |
| spin-orbit effective fields. However many aspects such as the angular and | |
| temperature dependent phenomena of the effective fields are little understood. | |
| Here, we evaluate the angular and temperature dependence of the current-induced | |
| spin-orbit effective fields considering contributions from both the anomalous | |
| and planar Hall effects. The longitudinal and transverse components of | |
| effective fields are found to have strong angular dependence on the | |
| magnetization direction at 300 K. The transverse field decreases significantly | |
| with decreasing temperature, whereas the longitudinal field shows weaker | |
| temperature dependence. Our results reveal important features and provide an | |
| opportunity for a more comprehensive understanding of current induced | |
| spin-orbit effective fields.",1404.1130v1 | |
| 2014-04-08,Ferromagnetic resonance spin pumping in CoFeB with highly resistive non-magnetic electrodes,"The relative contribution of spin pumping and spin rectification from the | |
| ferromagnetic resonance of CoFeB/non-magnetic bilayers was investigated as a | |
| function of non-magnetic electrode resistance. Samples with highly resistive | |
| electrodes of Ta or Ti exhibit a stronger spin rectification signal, which may | |
| result in over-(or under-)estimation of the spin Hall angle of the materials, | |
| while those with low resistive electrodes of Pt or Pd show the domination of | |
| the inverse spin Hall effect from spin pumping. By comparison with samples of | |
| single FM layer and an inverted structure, we provide a proper analysis method | |
| to extract spin pumping contribution.",1404.1993v1 | |
| 2014-05-02,Spin-orbit torque-driven magnetization switching and thermal effects studied in Ta\CoFeB\MgO nanowires,"We demonstrate magnetization switching in out-of-plane magnetized | |
| Ta\CoFeB\MgO nanowires by current pulse injection along the nanowires, both | |
| with and without a constant and uniform magnetic field collinear to the current | |
| direction. We deduce that an effective torque arising from spin-orbit effects | |
| in the multilayer drives the switching mechanism. While the generation of a | |
| component of the magnetization along the current direction is crucial for the | |
| switching to occur, we observe that even without a longitudinal field thermally | |
| generated magnetization fluctuations can lead to switching. Analysis using a | |
| generalized N\'eel-Brown model enables key parameters of the thermally induced | |
| spin-orbit torques switching process to be estimated, such as the attempt | |
| frequency and the effective energy barrier.",1405.0452v1 | |
| 2014-05-08,Controlling boron redistribution in CoFeB/MgO magnetic tunnel junctions during annealing by variation of cap layer materials and MgO deposition methods,"Magnetic tunnel junctions with crystalline MgO tunnel barrier and amorphous | |
| CoFeB electrodes received much attention due to their high tunnel magneto | |
| resistance ratio at room temperature. One important parameter for achieving | |
| high tunnel magneto resistance ratios is to control the boron diffusion from | |
| the electrodes especially during post growth annealing. By high resolution | |
| transmission electron microscopy and electron energy loss spectroscopy | |
| techniques we show that the cap layer material adjacent to the electrodes and | |
| the MgO deposition method are crucial to control boron redistribution. It is | |
| pointed out, that Ta cap layers acts as sinks for boron during annealing in | |
| contrast to Ru layers. Furthermore, radio frequency sputtered MgO tunneling | |
| barriers contain a rather high concentraion of boron in trigonal | |
| [BO$_3$]$^{3-}$ - environment after annealing in contrast to electron beam | |
| evaporated MgO which is virtually free from any boron. Our data further | |
| indicate that neither boron nor oxygen-vacancy-related gap states in the bulk | |
| of MgO barriers affect spin polarized transport for tunnel magneto resistance | |
| ratios at the level of 200%.",1405.1907v1 | |
| 2014-07-30,Room Temperature Spin Pumping in Topological Insulator Bi2Se3,"Three-dimensional (3D) topological insulators are known for their strong | |
| spin-orbit coupling and the existence of spin-textured topological surface | |
| states which could be potentially exploited for spintronics. Here, we | |
| investigate spin pumping from a metallic ferromagnet (CoFeB) into a 3D | |
| topological insulator (Bi2Se3) and demonstrate successful spin injection from | |
| CoFeB into Bi2Se3 and the direct detection of the electromotive force generated | |
| by the inverse spin Hal effect (ISHE) at room temperature. The spin pumping, | |
| driven by the magnetization dynamics of the metallic ferromagnet, introduces a | |
| spin current into the topological insulator layer, resulting in a broadening of | |
| the ferromagnetic resonance (FMR) linewidth. We find that the FMR linewidth | |
| more than quintuples, the spin mixing conductance can be as large as | |
| 3.4*10^20m^-2 and the spin Hall angle can be as large as 0.23 in the Bi2Se3 | |
| layer.",1407.7940v1 | |
| 2014-11-18,Towards wafer scale inductive characterization of spin transfer torque critical current density of magnetic tunnel junction stacks,"We explore the prospects of wafer scale inductive probing of the critical | |
| current density $j^{c0}$ for spin transfer torque switching of a | |
| CoFeB/MgO/CoFeB magnetic tunnel junction with varying MgO thickness. From | |
| inductive measurements magnetostatic parameters and the effective damping are | |
| derived and $j^{c0}$ is calculated based on spin transfer torque equations. The | |
| inductive values compare well to the values derived from current induced | |
| switching measurements on individual nanopillars. Using a wafer scale inductive | |
| probe head could in the future enable wafer probe station based metrology of | |
| $j^{c0}$.",1411.4868v1 | |
| 2015-04-25,Magnetic phase transitions in Ta/CoFeB/MgO multilayers,"We study thin films and magnetic tunnel junction nanopillars based on | |
| Ta/Co$_{20}$Fe$_{60}$B$_{20}$/MgO multilayers by electrical transport and | |
| magnetometry measurements. These measurements suggest that an ultrathin | |
| magnetic oxide layer forms at the Co$_{20}$Fe$_{60}$B$_{20}$/MgO interface. At | |
| approximately 160 K, the oxide undergoes a phase transition from an insulating | |
| antiferromagnet at low temperatures to a conductive weak ferromagnet at high | |
| temperatures. This interfacial magnetic oxide is expected to have significant | |
| impact on the magnetic properties of CoFeB-based multilayers used in spin | |
| torque memories.",1504.06716v1 | |
| 2015-05-21,Resistance minimum and electrical conduction mechanism in polycrystalline CoFeB thin films,"The temperature dependent resistance $R$($T$) of polycrystalline | |
| ferromagnetic CoFeB thin films of varying thickness are analyzed considering | |
| various electrical scattering processes. We observe a resistance minimum in | |
| $R$($T$) curves below $\simeq$ 29 K, which can be explained as an effect of | |
| intergranular Coulomb interaction in a granular system. The structural and | |
| Coulomb interaction related scattering processes contribute more as the film | |
| thickness decreases implying the role of disorder and granularity. Although the | |
| magnetic contribution to the resistance is the weakest compared to these two, | |
| it is the only thickness independent process. On the contrary, the negative | |
| coefficient of resistance can be explained by electron interaction effect in | |
| disordered amorphous films.",1505.05711v2 | |
| 2015-08-04,Scanning Kerr microscopy of current induced switching in Ta/CoFeB/MgO films with perpendicular magnetic anisotropy,"Ta/CoFeB/MgO trilayers with perpendicular magnetic anisotropy are expected to | |
| play a key role in the next generation of current and electric field switched | |
| memory and logic devices. In this study we use Kerr microscopy alongside | |
| electrical transport measurement to gain insight into the underlying switching | |
| mechanisms of such devices. We find switching to be a stochastic, domain wall | |
| driven process, the speed of which is strongly dependent on the switching | |
| current. Kerr imaging shows domain nucleation at the edge of the device which | |
| modelling reveals is likely assisted by the perpendicular component of the | |
| Oersted field. Further domain growth, leading to magnetisation reversal may be | |
| assisted by spin torques.",1508.00833v2 | |
| 2015-10-16,Enhanced orbital magnetic moments in magnetic heterostructures with interface perpendicular magnetic anisotropy,"We have studied the magnetic layer thickness dependence of the orbital | |
| magnetic moment in magnetic heterostructures to identify contributions from | |
| interfaces. Three different heterostructures, Ta/CoFeB/MgO, Pt/Co/AlO$_x$ and | |
| Pt/Co/Pt, which possess significant interface contribution to the perpendicular | |
| magnetic anisotropy, are studied as model systems. X-ray magnetic circular | |
| dichroism spectroscopy is used to evaluate the relative orbital moment, i.e. | |
| the ratio of the orbital to spin moments, of the magnetic elements constituting | |
| the heterostructures. We find that the relative orbital moment of Co in | |
| Pt/Co/Pt remains constant against its thickness whereas the moment increases | |
| with decreasing Co layer thickness for Pt/Co/AlO$_x$, suggesting that a | |
| non-zero interface orbital moment exists for the latter system. For | |
| Ta/CoFeB/MgO, a non-zero interface orbital moment is found only for Fe. X-ray | |
| absorption spectra shows that a particular oxidized Co state in Pt/Co/AlO$_x$, | |
| absent in other heterosturctures, may give rise to the interface orbital moment | |
| in this system. These results show element specific contributions to the | |
| interface orbital magnetic moments in ultrathin magnetic heterostructures.",1510.04756v1 | |
| 2015-12-02,Dynamic cantilever magnetometry of individual CoFeB nanotubes,"We investigate single CoFeB nanotubes with hexagonal cross-section using | |
| dynamic cantilever magnetometry (DCM). We develop both an analytical model | |
| based on the Stoner-Wohlfarth approximation and a broadly applicable numerical | |
| framework for analyzing DCM measurements of magnetic nanostructures. | |
| Magnetometry data show the presence of a uniformly magnetized configuration at | |
| high external fields with $\mu_0 M_s =1.3 \pm 0.1$ T and non-uniform | |
| configurations at low fields. In this low-field regime, comparison between | |
| numerical simulations and DCM measurements supports the existence of | |
| flux-closure configurations. Crucially, evidence of such configurations is only | |
| apparent because of the sensitivity of DCM to single nanotubes, whereas | |
| conventional measurements of ensembles are often obscured by sample-to-sample | |
| inhomogeneities in size, shape, and orientation",1512.00621v1 | |
| 2016-04-10,Interfacial Dzyaloshinskii-Moriya interaction in Pt/CoFeB films: effect of the heavy-metal thickness,"We report the observation of a Pt layer thickness dependence on the induced | |
| interfacial Dzyaloshinskii-Moriya interaction in ultra-thin | |
| Pt($d_{\text{Pt}}$)/CoFeB films. Taking advantage of the large spin-orbit | |
| coupling of the heavy metal, the interfacial Dzyaloshinskii-Moriya interaction | |
| is quantified by Brillouin light scattering measurements of the frequency | |
| non-reciprocity of spin-waves in the ferromagnet. The magnitude of the induced | |
| Dzyaloshinskii-Moriya coupling is found to saturate to a value $0.45$ | |
| mJ$/$m${}^2$ for Pt thicknesses larger than $\sim 2$ nm. The experimental | |
| results are explained by analytical calculations based on the 3-site indirect | |
| exchange mechanism that predicts a Dzyaloshinskii-Moriya interaction at the | |
| interface between a ferromagnetic thin layer and a heavy metal. Our findings | |
| open up a way to control and optimize chiral effects in ferromagnetic thin | |
| films through the thickness of the heavy metal layer.",1604.02626v2 | |
| 2016-04-14,THz-driven ultrafast spin-lattice scattering in amorphous metallic ferromagnets,"We use single-cycle THz fields and the femtosecond magneto-optical Kerr | |
| effect to respectively excite and probe the magnetization dynamics in two | |
| thin-film ferromagnets with different lattice structure: crystalline Fe and | |
| amorphous CoFeB. We observe Landau-Lifshitz-torque magnetization dynamics of | |
| comparable magnitude in both systems, but only the amorphous sample shows | |
| ultrafast demagnetization caused by the spin-lattice depolarization of the | |
| THz-induced ultrafast spin current. Quantitative modelling shows that such | |
| spin-lattice scattering events occur on similar time scales than the | |
| conventional spin conserving electronic scattering ($\sim30$ fs). This is | |
| significantly faster that optical laser-induced demagnetization. THz | |
| conductivity measurements point towards the influence of lattice disorder in | |
| amorphous CoFeB as the driving force for enhanced spin-lattice scattering.",1604.04077v1 | |
| 2016-04-26,Comparison of laser induced and intrinsic tunnel magneto-Seebeck effect in CoFeB/MgAl$_2$O$_4$ and CoFeB/MgO magnetic tunnel junctions,"We present a comparison of the tunnel magneto-Seebeck effect for laser | |
| induced and intrinsic heating. Therefore, | |
| Co$_{40}$Fe$_{40}$B$_{20}$/MgAl$_2$O$_4$ and Co$_{25}$Fe$_{55}$B$_{20}$/MgO | |
| magnetic tunnel junctions have been prepared. The TMS ratio of 3\,\% in case of | |
| the MAO MTJ agrees well with ratios found for other barrier materials, while | |
| the TMS ratio of 23\,\% of the MgO MTJ emphasizes the influence of the CoFe | |
| composition. We find results using the intrinsic method that differ in sign and | |
| magnitude in comparison to the results of the laser heating. The intrinsic | |
| contributions can alternatively be explained by the Brinkman model and the | |
| given junction properties. Especially, we are able to demonstrate that the | |
| symmetric contribution is solely influenced by the barrier asymmetry. Thus, we | |
| conclude that the symmetry analysis used for the intrinsic method is not | |
| suitable to unambiguously identify an intrinsic tunnel magneto-Seebeck effect.",1604.07569v2 | |
| 2016-05-23,Direct measurement of interfacial Dzyaloshinskii-Moriya interaction in X/CoFeB/MgO heterostructures with a scanning-NV magnetometer,"The Dzyaloshinskii-Moriya Interaction (DMI) has recently attracted | |
| considerable interest owing to its fundamental role in the stabilization of | |
| chiral spin textures in ultrathin ferromagnets, which are interesting | |
| candidates for future spintronic technologies. Here we employ a scanning | |
| nano-magnetometer based on a single nitrogen-vacancy (NV) defect in diamond to | |
| locally probe the strength of the interfacial DMI in CoFeB/MgO ultrathin films | |
| grown on different heavy metal underlayers X=Ta,TaN, and W. By measuring the | |
| stray field emanating from DWs in micron-long wires of such materials, we | |
| observe deviations from the Bloch profile for TaN and W underlayers that are | |
| consistent with a positive DMI value favoring right-handed chiral spin | |
| structures. Moreover, our measurements suggest that the DMI constant might vary | |
| locally within a single sample, illustrating the importance of local probes for | |
| the study of magnetic order at the nanoscale.",1605.07044v1 | |
| 2016-07-21,Effect of annealing on the interfacial Dzyaloshinskii-Moriya interaction in Ta/CoFeB/MgO trilayers,"The interfacial Dzyaloshinskii-Moriya interaction (DMI) has been shown to | |
| stabilize homochiral N\'eel-type domain walls in thin films with perpendicular | |
| magnetic anisotropy and as a result permit them to be propagated by a spin Hall | |
| torque. In this study, we demonstrate that in Ta/Co$_{20}$Fe$_{60}$B$_{20}$/MgO | |
| the DMI may be influenced by annealing. We find that the DMI peaks at | |
| $D=0.057\pm0.003$ mJ/m$^{2}$ at an annealing temperature of 230 $^{\circ}$C. | |
| DMI fields were measured using a purely field-driven creep regime domain | |
| expansion technique. The DMI field and the anisotropy field follow a similar | |
| trend as a function of annealing temperature. We infer that the behavior of the | |
| DMI and the anisotropy are related to interfacial crystal ordering and B | |
| expulsion out of the CoFeB layer as the annealing temperature is increased.",1607.06405v1 | |
| 2017-07-26,Reorientable Spin Direction for Spin Current Produced by the Anomalous Hall Effect,"We show experimentally that the spin direction of the spin current generated | |
| by spin-orbit interactions within a ferromagnetic layer can be reoriented by | |
| turning the magnetization direction of this layer. We do this by measuring the | |
| field-like component of spin-orbit torque generated by an exchange-biased FeGd | |
| thin film and acting on a nearby CoFeB layer. The relative angle of the CoFeB | |
| and FeGd magnetic moments is varied by applying an external magnetic field. We | |
| find that the resulting torque is in good agreement with predictions that the | |
| spin current generated by the anomalous Hall effect from the FeGd layer depends | |
| on the FeGd magnetization direction $\hat{m}_{FeGd}$ according to | |
| $\vec{\sigma}\propto\left ( \hat{y}\cdot \hat{m}_{FeGd} \right | |
| )\hat{m}_{FeGd}$, where $\hat{y}$ is the in-plane direction perpendicular to | |
| the applied charge current. Because of this angular dependence, the spin-orbit | |
| torque arising from the anomalous Hall effect can be non-zero in a sample | |
| geometry for which the spin Hall torque generated by non-magnetic materials is | |
| identically zero.",1707.08631v1 | |
| 2017-11-30,Domain Wall Motion Driven by Laplace Pressure in CoFeB-MgO Nanodots with Perpendicular Anisotropy,"We have studied the magnetization reversal of CoFeB-MgO nanodots with | |
| perpendicular anisotropy for size ranging from w=400 nm to 1 {\mu}m. Contrary | |
| to previous experiments, the switching field distribution is shifted toward | |
| lower magnetic fields as the size of the elements is reduced with a mean | |
| switching field varying as 1/w. We show that this mechanism can be explained by | |
| the nucleation of a pinned magnetic domain wall (DW) at the edges of the | |
| nanodots where damages are introduced by the patterning process. As the surface | |
| tension (Laplace pressure) applied on the DW increases when reducing the size | |
| of the nanodots, we demonstrate that the depinning field to reverse the entire | |
| elements varies as 1/w. These results suggest that the presence of DWs has to | |
| be considered in the switching process of nanoscale elements and open a path | |
| toward scalable spintronic devices.",1711.11334v2 | |
| 2018-03-08,CMOS compatible W/CoFeB/MgO spin Hall nano-oscillators with wide frequency tunability,"We demonstrate low-operational-current W/Co$_{20}$Fe$_{60}$B$_{20}$/MgO spin | |
| Hall nano-oscillators (SHNOs) on highly resistive silicon (HiR-Si) substrates. | |
| Thanks to a record high spin Hall angle of the $\beta$-phase W ($\theta_{SH}$ = | |
| -0.53), a very low threshold current density of 3.3 $\times$ 10$^{7}$ A/cm$^2$ | |
| can be achieved. Together with their very wide frequency tunability (7-28 GHz), | |
| promoted by a moderate perpendicular magnetic anisotropy, this makes | |
| HiR-Si/W/CoFeB based SHNOs potential candidates for wide-band microwave signal | |
| generation. Their CMOS compatibility offers a promising route towards the | |
| integration of spintronic microwave devices with other on-chip semiconductor | |
| microwave components.",1803.03032v1 | |
| 2018-06-13,Enhanced Spin-Orbit Torques and Magnetization Switching through Interface Engineering,"The origin of spin-orbit torques generated from the conversion of | |
| charge-to-spin currents is of considerable debate. Solid understanding of the | |
| physics behind is key to the development of current and voltage controlled | |
| switching dynamics in ultrathin heterostuctures. The field free switching | |
| observed recently (Phys. Rev. Lett. 120, 117703 (2018)) in a Pt/W/CoFeB | |
| structure has intensified such a debate. Here we derive a formula to evaluate a | |
| perpendicular effective field generated when the current flows through the | |
| heterostructure, considering the large resistivity difference between the two | |
| normal metal layers and the chemical potential gradient created at the | |
| interface. Together with recent X-ray photoelectron spectroscopy findings at | |
| the interface of a Pd/CoFeB structure, we conclude that a new torque generated | |
| may play a key role in the field free switching. The model and mechanism | |
| proposed agrees with previous reports on spin current injection and field free | |
| switching using different interface engineering methods.",1806.05163v1 | |
| 2018-06-20,Domain wall resistance in CoFeB-based heterostructures with interface Dzyaloshinskii-Moriya interaction,"We have studied the domain wall resistance in W/Ta/CoFeB/MgO | |
| heterostructures. The Ta layer thickness is varied to control the type of | |
| domain walls via changes in the interfacial Dzyaloshinskii Moriya interaction. | |
| We find a nearly constant domain wall resistance against the Ta layer | |
| thickness. Adding contributions from the anisotropic magnetoresistance, spin | |
| Hall magnetoresistance and anomalous Hall effect describe well the domain wall | |
| resistance of the thick Ta layer films. However, a discrepancy remains for the | |
| thin Ta layer films wherein chiral N\'eel-like domain walls are found. These | |
| results show the difficulty of studying the domain wall type from resistance | |
| measurements.",1806.07750v1 | |
| 2018-11-13,Spin-orbit torques acting upon a perpendicularly-magnetized Py layer,"We show that Py, a commonly-used soft ferromagnetic material with weak | |
| anisotropy, can become perpendicularly-magnetized while depositing on Ta buffer | |
| layer with Hf or Zr insertion layers (ILs) and MgO capping layer. By using two | |
| different approaches, namely harmonic voltage measurement and hysteresis loop | |
| shift measurement, the dampinglike spin-orbit torque (DL-SOT) efficiencies from | |
| Ta/IL/Py/IL/MgO magnetic heterostructures with perpendicular magnetic | |
| anisotropy are characterized. We find that though Ta has a significant spin | |
| Hall effect, the DL-SOT efficiencies are small in systems with the Ta/Py | |
| interface compared to that obtained from the control sample with the | |
| traditional Ta/CoFeB interface. Our results indicate that the spin transparency | |
| for the Ta/Py interface is much less than that for the Ta/CoFeB interface, | |
| which might be related to the variation of spin mixing conductance for | |
| different interfaces.",1811.05164v1 | |
| 2017-04-01,Thermally nucleated magnetic reversal in CoFeB/MgO nanodots,"Power consumption is the main limitation in the development of new high | |
| performance random access memory for portable electronic devices. Magnetic RAM | |
| (MRAM) with CoFeB/MgO based magnetic tunnel junctions (MTJs) is a promising | |
| candidate for reducing the power consumption given its non-volatile nature | |
| while achieveing high performance. The dynamic properties and switching | |
| mechanisms of MTJs are critical to understanding device operation and to enable | |
| scaling of devices below 30 nm in diameter. Here we show that the magnetic | |
| reversal mechanism is incoherent and that the switching is thermally nucleated | |
| at device operating temperatures. Moreover, we find an intrinsic thermal | |
| switching field distribution arising on the sub-nanosecond timescale even in | |
| the absence of size and anisotropy distributions or material defects. These | |
| features represent the characteristic signature of the dynamic properties in | |
| MTJs and give an intrinsic limit to reversal reliability in small magnetic | |
| nanodevices.",1704.00106v1 | |
| 2017-05-13,"Tuning the perpendicular magnetic anisotropy, spin Hall switching current density and domain wall velocity by submonolayer insertion in Ta / CoFeB / MgO heterostructures","By submonolayer insertion of Au, Pt, or Pd into Ta / CoFeB / MgO / Ta | |
| heterostructures we tune the perpendicular magnetic anisotropy and the coercive | |
| field of the ferromagnetic layer. We demonstrate that this has a major | |
| influence on the spin Hall switching current density and its dependence on the | |
| external magnetic field. Despite a rather small effective spin Hall angle of | |
| $\theta_\mathrm{SH} \approx -0.07$, we obtain switching current densities as | |
| low as $2 \times 10^{10}$ A/m$^2$ with a 2 \AA{} Au interlayer. We find that | |
| the Dzyaloshinskii-Moriya interaction parameter $D$ is reduced with Au or Pd | |
| interlayers, and the perpendicular anisotropy field is reduced by an order of | |
| magnitude with the Pd interlayer. The dependence of the switching current | |
| density on the current pulse width is quantitatively explained with a domain | |
| wall nucleation and propagation model. Interface engineering is thus found to | |
| be a suitable route to tailor the current-induced magnetization switching | |
| properties of magnetic heterostructures.",1705.04800v1 | |
| 2019-10-17,Planar Hall driven torque in a FM/NM/FM system,"An important goal of spintronics is to covert a charge current into a spin | |
| current with a controlled spin polarization that can exert torques on an | |
| adjacent magnetic layer. Here we demonstrate such torques in a two ferromagnet | |
| system. A CoNi multilayer is used as a spin current source in a sample with | |
| structure CoNi/Au/CoFeB. Spin torque ferromagnetic resonance is used to measure | |
| the torque on the CoFeB layer. The response as a function of the applied field | |
| angle and current is consistent with the symmetry expected for a torques | |
| produced by the planar Hall effect originating in CoNi. We find the strength of | |
| this effect to be comparable to that of the spin Hall effect in platinum, | |
| indicating that the planar Hall effect holds potential as a spin current source | |
| with a controllable polarization direction.",1910.08039v1 | |
| 2019-06-14,Mechanisms of FMR line broadening in CoFeB-LiNbO$_3$ granular films in the vicinity of metal-insulator transition,"Metal-insulator (CoFeB)$_x$(LiNbO$_3$)$_{100-x}$ nanocomposite films with | |
| different content of the ferromagnetic (FM) phase $x$ are investigated by | |
| ferromagnetic resonance (FMR) technique. A strong change of the FMR line shape | |
| is observed in the vicinity of metal-insulator transition (MIT) of the film, | |
| where the hopping-type conductivity $\sigma$ modifies to the regime of a strong | |
| intergranular tunnelling, characterized by a logarithmic dependence $\sigma(T)$ | |
| at high temperatures. It is shown that below MIT, the FMR linewidth is mainly | |
| determined by the inhomogeneous distribution of the local anisotropy axes in | |
| the film plane. Above MIT, the contribution of this inhomogeneity to the line | |
| broadening decreases. At the same time, two-magnon magnetic relaxation | |
| processes begin to play a significant role in the formation of the linewidth. | |
| The observed behaviour indicates the critical role of interparticle exchange in | |
| the tunnelling regime above MIT of the nanocomposite.",1906.06320v2 | |
| 2020-04-03,Modulation of field-like spin orbit torque in heavy metal / ferromagnet heterostructure,"Recent studies rediscovered the crucial role of field-like spin orbit torque | |
| (SOT) in nanosecond-timescale SOT dynamics. However, there is not yet an | |
| effective way to control its relative amplitude. Here, we experimentally | |
| modulate the field-like SOT in W/CoFeB/MgO trilayers through tuning the | |
| interfacial spin accumulation. By performing spin Hall magnetoresistance | |
| measurement, we find that the CoFeB with enhanced spin dephasing, either | |
| generated from larger layer thickness or from proper annealing, can distinctly | |
| boost the spin absorption and enhance the interfacial spin mixing conductance | |
| G_r. While the damping-like torque efficiency increases with G_r, the | |
| field-like torque efficiency turns out to decrease with it. The results suggest | |
| that the interfacial spin accumulation, which largely contributes to a | |
| field-like torque, is reduced by higher interfacial spin transparency. Our work | |
| shows a new path to further improve the performance of SOT-based magnetic | |
| devices.",2004.01357v1 | |
| 2020-04-29,Terahertz Emission From an Exchange-Coupled Synthetic Antiferromagnet,"We report on terahertz emission from FeMnPt/Ru/FeMnPt and | |
| Pt/CoFeB/Ru/CoFeB/Pt synthetic antiferromagnet (SAF) structures upon | |
| irradiation by a femtosecond laser; the former is via the anomalous Hall | |
| effect, whereas the latter is through the inverse spin Hall effect. The | |
| antiparallel alignment of the two ferromagnetic layers leads to a terahertz | |
| emission peak amplitude that is almost double that for a corresponding | |
| single-layer or bilayer emitter with the same equivalent thickness. In | |
| addition, we demonstrate by both simulation and experiment that terahertz | |
| emission provides a powerful tool to probe the magnetization reversal processes | |
| of individual ferromagnetic layers in a SAF structure, as the terahertz signal | |
| is proportional to the vector difference of the magnetizations of the two | |
| ferromagnetic layers.",2004.14128v1 | |
| 2020-05-11,Improving thermal stability of MnN/CoFeB exchange bias systems by optimizing the Ta buffer layer,"We investigated the influence of the Ta buffer layer on the thermal stability | |
| of polycrystalline Ta/ MnN/ CoFeB exchange bias systems, showing high exchange | |
| bias of about 1800 Oe at room temperature. The thermal stability of those | |
| trilayer systems is limited by nitrogen diffusion that occurs during annealing | |
| processes. Most of the nitrogen diffuses into the Ta buffer layer, which is | |
| necessary for good crystal growth of MnN and thus a crucial component of the | |
| exchange bias system. In order to improve the thermal stability, we prepared | |
| exchange bias stacks where we varied the Ta thickness to look for an optimum | |
| value that guarantees stable and high exchange over a broad temperature range. | |
| Our findings show that thin layers of 2-5 nm Ta indeed support stable exchange | |
| bias up to annealing temperatures of more than $550^{\circ}$C. Furthermore, we | |
| found that the introduction of a TaN$_{\text{x}}$ layer between MnN and Ta, | |
| acting as a barrier, can prevent nitrogen diffusion. However, our results show | |
| that those measures, even though being beneficial in terms of thermal | |
| stability, often lead to decreased crystallinity and thus lower the exchange | |
| bias.",2005.05166v1 | |
| 2017-02-24,Giant perpendicular exchange bias with antiferromagnetic MnN,"We investigated an out-of-plane exchange bias system that is based on the | |
| antiferromagnet MnN. Polycrystalline, highly textured film stacks of Ta / MnN / | |
| CoFeB / MgO / Ta were grown on SiO$_x$ by (reactive) magnetron sputtering and | |
| studied by x-ray diffraction and Kerr magnetometry. Nontrivial modifications of | |
| the exchange bias and the perpendicular magnetic anisotropy were observed both | |
| as functions of film thicknesses as well as field cooling temperatures. In | |
| optimized film stacks, a giant perpendicular exchange bias of 3600 Oe and a | |
| coercive field of 350 Oe were observed at room temperature. The effective | |
| interfacial exchange energy is estimated to be $J_\mathrm{eff} = 0.24$ mJ/m$^2$ | |
| and the effective uniaxial anisotropy constant of the antiferromagnet is | |
| $K_\mathrm{eff} = 24$ kJ/m$^3$. The maximum effective perpendicular anisotropy | |
| field of the CoFeB layer is $H_\mathrm{ani} = 3400$ Oe. These values are larger | |
| than any previously reported values. These results possibly open a route to | |
| magnetically stable, exchange biased perpendicularly magnetized spin valves.",1702.07538v2 | |
| 2019-05-22,Reduced Exchange Interactions in Magnetic Tunnel Junction Free Layers with Insertion Layers,"Perpendicularly magnetized CoFeB layers with ultra-thin non-magnetic | |
| insertion layers are very widely used as the electrodes in magnetic tunnel | |
| junctions for spin transfer magnetic random access memory devices. Exchange | |
| interactions play a critical role in determining the thermal stability of | |
| magnetic states in such devices and their spin torque switching efficiency. | |
| Here the exchange constant of free layers incorporated in full magnetic tunnel | |
| junction layer stacks, specifically CoFeB free layers with W insertion layers | |
| is determined by magnetization measurements in a broad temperature range. A | |
| significant finding is that the exchange constant decreases significantly and | |
| abruptly with W insertion layer thickness. The perpendicular magnetic | |
| anisotropy shows the opposite trend; it initially increases with W insertion | |
| layer thickness and shows a broad maximum for approximately one monolayer (0.3 | |
| nm) of W. These results highlight the interdependencies of magnetic | |
| characteristics required to optimize the performance of magnetic tunnel | |
| junction devices.",1905.09329v1 | |
| 2019-08-06,Superparamagnetic dwell times and tuning of switching rates in perpendicular CoFeB/MgO/CoFeB tunnel junctions,"Thin electrodes of magnetic tunnel junctions can show superparamagnetism at | |
| surprisingly low temperature. We analysed their thermally induced switching for | |
| varying temperature, magnetic and electric field. Although the dwell times | |
| follow an Arrhenius law, they are orders of magnitude too small compared to a | |
| model of single domain activation. Including entropic effects removes this | |
| inconsistency and leads to a magnetic activation volume much smaller than that | |
| of the electrode. Comparing data for varying barrier thickness then allows to | |
| separate the impact of Zeman energy, spin-transfer-torque and voltage induced | |
| anisotropy change on the dwell times. Based on these results, we demonstrate a | |
| tuning of the switching rates by combining magnetic and electric fields, which | |
| opens a path for their application in noisy neural networks.",1908.02139v3 | |
| 2019-09-06,Effect of Tantalum spacer thickness and deposition conditions on the properties of MgO/CoFeB/Ta/CoFeB/MgO free layers,"To get stable perpendicularly magnetized tunnel junctions at small device | |
| dimensions, composite free layers that comprise two MgO/FeCoB interfaces as | |
| sources of interface anisotropy are generally used. Proper cristallisation and | |
| annealing robustness is typically ensured by the insertion of a spacer layer of | |
| the early transition metal series within the FeCoB layer. We study the | |
| influence of the spacer thickness and growth condition on the switching metrics | |
| of tunnel junctions thermally annealed at 400$^\circ$C for the case of 1-4 | |
| \r{A} Ta spacers. Thick Ta spacer results in a large anisotropies indicative of | |
| a better defined top FeCoB/MgO interface, but this is achieved at the | |
| systematic expense of a stronger damping. For the best anisotropy-damping | |
| compromise, junctions of diameter 22 nm can still be stable and spin-torque | |
| switched. Coercivity and inhomogeneous linewidth broadening, likely arising | |
| from roughness at the FeCoB/Ta interface, can be reduced if a sacrificial Mg | |
| layer is inserted before the Ta spacer deposition.",1909.02741v1 | |
| 2020-02-16,Electric-field control of spin-orbit torques in perpendicularly magnetized W/CoFeB/MgO films,"Controlling magnetism by electric fields offers a highly attractive | |
| perspective for designing future generations of energy-efficient information | |
| technologies. Here, we demonstrate that the magnitude of current-induced | |
| spin-orbit torques in thin perpendicularly magnetized CoFeB films can be tuned | |
| and even increased by electric field generated piezoelectric strain. Using | |
| theoretical calculations, we uncover that the subtle interplay of spin-orbit | |
| coupling, crystal symmetry, and orbital polarization is at the core of the | |
| observed strain dependence of spin-orbit torques. Our results open a path to | |
| integrating two energy efficient spin manipulation approaches, the electric | |
| field-induced strain and the current-induced magnetization switching, thereby | |
| enabling novel device concepts.",2002.06578v1 | |
| 2020-10-31,Effect of spin glass frustration on exchange bias in NiMn/CoFeB bilayers,"Exchange bias in ferromagnetic/antiferromagnetic systems can be explained in | |
| terms of various interfacial phenomena. Among these spin glass frustration can | |
| affect the magnetic properties in exchange bias systems. Here we have studied a | |
| NiMn/CoFeB exchange bias system in which spin glass frustration seems to play a | |
| crucial role. In order to account the effect of spin glass frustration on | |
| magnetic properties, we have performed the temperature and cooling field | |
| dependence of exchange bias. We have observed the decrease of exchange bias | |
| field (HEB) with cooling field (HFC) whereas there is not significant effect on | |
| coercive field (HC). Exponential decay of HEB and HC is found in these exchange | |
| bias systems. Further, training effect measurements have been performed to | |
| study the spin relaxation mechanism. We have fitted the training effect data | |
| with frozen and rotatable spin relaxation model. We have investigated the ratio | |
| of relaxation rate of interfacial rotatable and frozen spins in this study. The | |
| training effect data are also fitted with various other models. Further, we | |
| observed the shifting of peak temperature towards higher temperature with | |
| frequency from the ac susceptibility data.",2011.00188v1 | |
| 2021-01-18,Magnetization switching induced by spin-orbit torque from Co2MnGa magnetic Weyl semimetal thin films,"This study reports the magnetization switching induced by spin-orbit torque | |
| (SOT) from the spin current generated in Co2MnGa magnetic Weyl semimetal (WSM) | |
| thin films. We deposited epitaxial Co2MnGa thin films with highly B2-ordered | |
| structure on MgO(001) substrates. The SOT was characterized by harmonic Hall | |
| measurements in a Co2MnGa/Ti/CoFeB heterostructure and a relatively large spin | |
| Hall efficiency of -7.8% was obtained.The SOT-induced magnetization switching | |
| of the perpendicularly magnetized CoFeB layer was further demonstrated using | |
| the structure. The symmetry of second harmonic signals, thickness dependence of | |
| spin Hall efficiency, and shift of anomalous Hall loops under applied currents | |
| were also investigated. This study not only contributes to the understanding of | |
| the mechanisms of spin-current generation from magnetic-WSM-based | |
| heterostructures, but also paves a way for the applications of magnetic WSMs in | |
| spintronic devices.",2101.06881v1 | |
| 2021-02-07,Spinterface Induced Modification in Magnetic Properties in Co40Fe40B20/Fullerene Bilayers,"Organic semiconductor/ferromagnetic bilayer thin films can exhibit novel | |
| properties due to the formation of the spinterface at the interface. | |
| Buckminsterfullerene (C60) has been shown to exhibit ferromagnetism at the | |
| interface when it is placed next to a ferromagnet (FM) such as Fe or Co. | |
| Formation of spinterface occurs due to the orbital hybridization and spin | |
| polarized charge transfer at the interface. In this work, we have demonstrated | |
| that one can enhance the magnetic anisotropy of the low Gilbert damping alloy | |
| CoFeB by introducing a C60 layer. We have shown that anisotropy increases by | |
| increasing the thickness of C60 which might be a result of the formation of | |
| spinterface. However, the magnetic domain structure remains same in the bilayer | |
| samples as compared to the reference CoFeB film.",2102.03914v4 | |
| 2021-05-06,Interfacial and bulk spin Hall contributions to field-like spin-orbit torque generated by Iridium,"We present measurements of spin orbit torques generated by Ir as a function | |
| of film thickness in sputtered Ir/CoFeB and Ir/Co samples. We find that Ir | |
| provides a damping-like component of spin orbit torque with a maximum spin | |
| torque conductivity 1.4e5 in SI unit and a maximum spin-torque efficiency of | |
| 0.04, which is sufficient to drive switching in an 0.8 nm film of CoFeB with | |
| perpendicular magnetic anisotropy. We also observe a surprisingly large field | |
| like spin orbit torque. Measurements as a function of Ir thickness indicate a | |
| substantial contribution to the FLT from an interface mechanism so that in the | |
| ultrathin limit there is a non-zero FLT with a maximum torque conductivity | |
| -5.0E4 in the SI unit. When the Ir film thickness becomes comparable to or | |
| greater than its spin diffusion length, 1.6 nm, there is also a smaller bulk | |
| contribution to the fieldlike torque.",2105.02787v1 | |
| 2021-06-04,Driving skyrmions with low threshold current density in Pt/CoFeB thin film,"Magnetic skyrmions are topologically stable spin swirling particle like | |
| entities which are appealing for next generation spintronic devices. The | |
| expected low critical current density for the motion of skyrmions makes them | |
| potential candidates for future energy efficient electronic devices. Several | |
| heavy metal/ferromagnetic (HM/FM) systems have been explored in the past decade | |
| to achieve faster skyrmion velocity at low current densities. In this context, | |
| we have studied Pt/CoFeB/MgO heterostructures in which skyrmions have been | |
| stabilized at room temperature (RT). It has been observed that the shape of the | |
| skyrmions are perturbed even by the small stray field arising from low moment | |
| magnetic tips while performing the magnetic force microscopy (MFM), indicating | |
| presence of low pinning landscape in the samples. This hypothesis is indeed | |
| confirmed by the low threshold current density to drive the skyrmions in our | |
| sample, at velocities of few 10m/s.",2106.02407v3 | |
| 2021-08-16,Highly fcc-textured Pt-Al alloy films grown on MgO(001) showing enhanced spin Hall efficiency,"We report on a systematic comparative study of the spin Hall efficiency | |
| between highly face-centered cubic (fcc)-textured Pt-Al alloy films grown on | |
| MgO(001) and poorly-crystallized Pt-Al alloy films grown on SiO$_2$. Using | |
| CoFeB as the detector, we show that for Al compositions centering around $x = | |
| 25$, mainly L1$_{2}$ ordered Pt$_{100-x}$Al$_x$ alloy films grown on MgO | |
| exhibit outstanding charge-spin conversion efficiency. For | |
| Pt$_{78}$Al$_{22}$/CoFeB bilayer on MgO, we obtain damping-like spin Hall | |
| efficiency as high as $\xi_\textrm{DL} \sim +0.20$ and expect up to seven-fold | |
| reduction of power consumption compared to the polycrystalline bilayer of the | |
| same Al composition on SiO$_2$. This work demonstrates that improving the | |
| crystallinity of fcc Pt-based alloys is a crucial step for achieving large spin | |
| Hall efficiency and low power consumption in this material class.",2108.06927v1 | |
| 2021-08-23,Reconfigurable 3D magnonic crystal: tunable and localized spin-wave excitations in CoFeB meander-shaped film,"In this work, we study experimentally by broadband ferromagnetic resonance | |
| measurements, the dependence of the spin-wave excitation spectra on the | |
| magnetic applied field in CoFeB meander-shaped films. Two different | |
| orientations of the external magnetic field were explored, namely parallel or | |
| perpendicular to the lattice cores. The interpretation of the field dependence | |
| of the frequency and spatial profiles of major spin-wave modes were obtained by | |
| micromagnetic simulations. We show that the vertical segments lead to the | |
| easy-axis type of magnetic anisotropy and support the in-phase and out-of-phase | |
| spin-wave precession amplitude in the vertical segments. The latter could | |
| potentially be used for the design of tunable metasurfaces or in magnetic | |
| memories based on meandering 3D magnetic films.",2108.10232v1 | |
| 2021-11-16,Energy-efficient W$_{\text{100-x}}$Ta$_{\text{x}}$/CoFeB/MgO spin Hall nano-oscillators,"We investigate a W-Ta alloying route to reduce the auto-oscillation current | |
| densities and the power consumption of nano-constriction based spin Hall nano | |
| oscillators. Using spin-torque ferromagnetic resonance (ST-FMR) measurements on | |
| microbars of W$_{\text{100-x}}$Ta$_{\text{x}}$(5 nm)/CoFeB(t)/MgO stacks with t | |
| = 1.4, 1.8, and 2.0 nm, we measure a substantial improvement in both the | |
| spin-orbit torque efficiency and the spin Hall conductivity. We demonstrate a | |
| 34\% reduction in threshold auto-oscillation current density, which translates | |
| into a 64\% reduction in power consumption as compared to pure W-based SHNOs. | |
| Our work demonstrates the promising aspects of W-Ta alloying for the | |
| energy-efficient operation of emerging spintronic devices.",2111.08627v1 | |
| 2021-12-23,Electric-field-induced parametric excitation of exchange magnons in a CoFeB/MgO junction,"Electric-field controlled magnetization dynamics is an important integrant in | |
| low power spintronic devices. In this letter, we demonstrate electric-field | |
| induced parametric excitation for CoFeB/MgO junctions by using interfacial | |
| in-plane magnetic anisotropy. When the in-plane magnetic anisotropy and the | |
| external magnetic field are parallel to each other, magnons are efficiently | |
| excited by using electric-field induced parametric excitation. Its wavelength | |
| and wavenumber are tuned by changing input power and frequency of the applied | |
| voltage. A generalized phenomenological model is developed to explain the | |
| underlying role of the electric-field torque. Electrical excitation with no | |
| Joule heating offers a good opportunity for developing magnonic devices and | |
| exploring various nonlinear dynamics in magnetic systems.",2112.12308v2 | |
| 2022-03-17,Symmetry effects on the static and dynamic properties of coupled magnetic oscillators,"The effect of symmetry on the resonance spectra of antiferromagnetically | |
| coupled oscillators has attracted new interest with the discovery of | |
| symmetry-breaking induced anti-crossings. Here, we experimentally characterise | |
| the resonance spectrum of a synthetic antiferromagnet Pt/CoFeB/Ru/CoFeB/Pt, | |
| where we are able to independently tune the effective magnetisation of the two | |
| coupled magnets. To model our results we apply the mathematical methods of | |
| group theory to the solutions of the Landau Lifshitz Gilbert equation. This | |
| general approach, usually applied to quantum mechanical systems, allows us to | |
| identify the main features of the resonance spectrum in terms of symmetry | |
| breaking and to make a direct comparison with crystal antiferromagnets.",2204.01490v1 | |
| 2022-04-25,Ab-initio study of magneto-ionic mechanisms in ferromagnet/oxide multilayers,"The application of gate voltages in heavy metal/ferromagnet/Oxide multilayer | |
| stacks has been identified as one possible candidate to manipulate their | |
| anisotropy at will. However, this method has proven to show a wide variety of | |
| behaviours in terms of reversibility, depending on the nature of the | |
| metal/oxide interface and its degree of oxidation. In order to shed light on | |
| the microscopic mechanism governing the complex magneto-ionic behaviour in | |
| $\text{Ta/CoFeB/}\text{HfO}_2$, we perform ab-initio simulations on various | |
| setups comprising $\text{Fe/O, Fe/HfO}_2$ interfaces with different oxygen atom | |
| interfacial geometries. After the determination of the more stable interfacial | |
| configurations, we calculate the magnetic anisotropy energy on the different | |
| unit cell configurations and formulate a possible mechanism that well describes | |
| the recent experimental observations in $\text{Ta/CoFeB/}\text{HfO}_2$.",2204.11699v1 | |
| 2022-06-21,Extrinsic tunnel Hall effect in CoFeB/MgO/Pt junctions,"The Hall effect that occurs when current flows through a CoFeB/MgO/Pt tunnel | |
| junction is investigated. It is shown that the transverse voltage in Pt | |
| electrode is nonlinear on a DC voltage applied to the tunnel junction. It has | |
| both linear (odd) and quadratic (even) parts. The linear part contains | |
| well-known contributions of the anomalous Hall effect in the ferromagnetic | |
| electrode, inverse spin-hall effect in platinum and others. The quadratic part | |
| is a phenomenon caused by the spin-orbit scattering of electrons in an external | |
| electric field induced by a voltage applied to the barrier. This field reaches | |
| values of $10^9$ V/m which is close to internal atomic fields. The magnitude of | |
| both effects decreases as thickness of Pt electrode is increased due to | |
| shunting effects.",2206.10264v1 | |
| 2023-06-08,Unidirectionality of spin waves in Synthetic Antiferromagnets,"We study the frequency non-reciprocity of the spin waves in symmetric | |
| CoFeB/Ru/CoFeB synthetic antiferromagnets stacks set in the scissors state by | |
| in-plane applied fields. Using a combination of Brillouin Light Scattering and | |
| propagating spin wave spectroscopy experiments, we show that the acoustical | |
| spin waves in synthetic antiferromagnets possess a unique feature if their | |
| wavevector is parallel to the applied field: the frequency non-reciprocity due | |
| to layer-to-layer dipolar interactions can be so large that the acoustical spin | |
| waves transfer energy in a unidirectional manner for a wide and bipolar | |
| interval of wavevectors. Analytical modeling and full micromagnetic | |
| calculations are conducted to account for the dispersion relations of the | |
| optical and acoustical spin waves for arbitrary field orientations. Our | |
| formalism provides a simple and direct method to understand and design devices | |
| harnessing unidirectional propagation of spin waves in synthetic | |
| antiferromagnets.",2306.05259v2 | |
| 2024-03-13,Theoretical limits of magnetic detection of structural surface defects at the nanometer scale,"We present a theoretical study on the magnetic signals of structural surface | |
| defects like cracks or indents combined with rough surfaces or subsurface | |
| inclusions of soft ferromagnetic metals like body-centered cubic Fe or | |
| amorphous CoFeB. We discuss limits of early detection of small surface defects | |
| on the basis of calculated magnetic stray fields few tens of nm above the | |
| surface. The considered surface imperfections have extensions of a few nm which | |
| correspond to low multiples of the magnetic exchange lengths of Fe or CoFeB. | |
| The detection of such small inhomogeneities requires that the sensor is about | |
| as close to the surface as the size of the inhomogeneity is. Furthermore, the | |
| step width of a scanning sensor must be of the same size as well. Both these | |
| requirements may be fulfilled for instance by scanning microscopy with diamond | |
| nitrogen-vacancy-center quantum sensors.",2403.08412v1 | |
| 2005-10-18,"Domain imaging, MOKE and magnetoresistance studies of CoFeB films for MRAM applications","We present a detailed study on domain imaging, Kerr effect magnetometry | |
| (MOKE) and magnetoresistance (MR), for a series of 20 nm | |
| Co$_{73.8}$Fe$_{16.2}$B$_{10}$ thin films, both as-deposited (amorphous) and | |
| annealed (crystalline). By considering the two different (orthogonal) in-plane | |
| magnetization components, obtained by MOKE measurements, we were able to study | |
| the uniaxial anisotropy induced during CoFeB-deposition and to discriminate the | |
| magnetization processes under a magnetic field parallel and perpendicular to | |
| such axis. MOKE magnetic imaging enabled us to observe the dominant | |
| magnetization processes, namely domain wall motion and moment rotation. These | |
| processes were correlated with the behavior of the magnetoresistance, which | |
| depends both on short-range spin disorder electron scattering and on the angle | |
| between the electrical current and the spontaneous magnetization | |
| ($\emph{\textbf{M}}_{S}$). A simple numerical treatment based on | |
| Stoner-Wolfarth model enables us to satisfactorily predict the magnetization | |
| behaviour observed in these films. A comparison between the results in | |
| Co$_{73.8}$Fe$_{16.2}$B$_{10}$ films and the previous ones obtained in annealed | |
| Co$_{80}$Fe$_{20}$ films, show that the introduction of boron in CoFe reduces | |
| significatively the coercive and saturation fields along the easy axis (e.g. | |
| $H_{c}$ from $\sim$ 2 down to $\sim$ 0.5 kAm$^{-1}$). Also, the magnetization | |
| along the hard axis saturates at lower fields. We conclude that amorphous and | |
| nanocrystalline CoFeB films show low coercive fields and abrupt switching, as | |
| well as absence of short range spin disorder effects after switching when | |
| compared with Co$_{80}$Fe$_{20}$.",0510479v2 | |
| 2014-05-05,On/off switching of bit readout in bias-enhanced tunnel magneto-Seebeck effect,"Thermoelectric effects in magnetic tunnel junctions are currently an | |
| attractive research topic. Here, we demonstrate that the tunnel magneto-Seebeck | |
| effect (TMS) in CoFeB/MgO/CoFeB tunnel junctions can be switched on to a logic | |
| 1 state and off to 0 by simply changing the magnetic state of the CoFeB | |
| electrodes. We enable this new functionality of magnetic tunnel junctions by | |
| combining a thermal gradient and an electric field. This new technique unveils | |
| the bias-enhanced tunnel magneto-Seebeck effect, which can serve as the basis | |
| for logic devices or memories in a green information technology with a pure | |
| thermal write and read process. Furthermore, the thermally generated voltages | |
| that are referred to as the Seebeck effect are well known to sensitively depend | |
| on the electronic structure and therefore have been valued in solid-state | |
| physics for nearly one hundred years. Here, we lift Seebeck's historic | |
| discovery from 1821 to a new level of current spintronics. Our results show | |
| that the signal crosses zero and can be adjusted by tuning a bias voltage that | |
| is applied between the electrodes of the junction; hence, the name of the | |
| effect is bias-enhanced tunnel magneto-Seebeck effect (bTMS). Via the spin- and | |
| energy-dependent transmission of electrons in the junction, the bTMS effect can | |
| be configured using the bias voltage with much higher control than the tunnel | |
| magnetoresistance (TMR) and even completely suppressed for only one magnetic | |
| configuration, which is either parallel (P) or anti-parallel (AP). This option | |
| allows a readout contrast for the magnetic information of -3000% at room | |
| temperature while maintaining a large signal for one magnetic orientation. This | |
| contrast is much larger than the value that can be obtained using the TMR | |
| effect. Moreover, our measurements are a step towards the experimental | |
| realization of high TMS ratios, which are predicted for specific Co-Fe | |
| compositions.",1405.1064v1 | |
| 2020-05-08,Nanoscale Spin Injector Driven by a Microwave Voltage,"We propose an electrically driven spin injector into normal metals and | |
| semiconductors, which is based on a magnetic tunnel junction (MTJ) subjected to | |
| a microwave voltage. Efficient functioning of such an injector is provided by | |
| electrically induced magnetization precession in the ""free"" layer of MTJ, which | |
| generates the spin pumping into a metallic or semiconducting overlayer. We | |
| theoretically describe the spin and charge dynamics in the | |
| CoFeB/MgO/CoFeB/Au(GaAs) heterostructures. First, the magnedynamics in the free | |
| CoFeB layer is quantified with the account of a spin-transfer torque and a | |
| voltage-controlled magnetic anisotropy. By numerically solving the | |
| magnetodynamics equation, we determine dependences of the precession amplitude | |
| on the frequency $f$ and magnitude $V_\mathrm{max}$ of the ac voltage applied | |
| to the MTJ. It is found that the frequency dependence changes drastically above | |
| the threshold amplitude $V_\mathrm{max} \approx 200$mV, exhibiting a break at | |
| the resonance frequency $f_\mathrm{res}$ due to nonlinear effects. The results | |
| obtained for the magnetization dynamics are used to describe the spin injection | |
| and pumping into the Au and GaAs overlayers. Since the generated spin current | |
| creates additional charge current owing to the inverse spin Hall effect, we | |
| also calculate distribution of the electric potential in the thick Au | |
| overlayer. The calculations show that the arising transverse voltage becomes | |
| experimentally measurable at $f = f_\mathrm{res}$. Finally, we evaluate the | |
| spin accumulation in a long n$^+$-GaAs bar coupled to the MTJ and determine its | |
| temporal variation and spatial distribution along the bar. It is found that the | |
| spin accumulation under resonant excitation is large enough for experimental | |
| detection even at micrometer distances from the MTJ. This result demonstrates | |
| high efficiency of the described nanoscale spin injector.",2005.03896v1 | |
| 2019-12-08,Thermal Conductivity of Oxide Tunnel Barriers in Magnetic Tunnel Junctions Measured by Ultrafast Thermoreflectance and Magneto-optic Kerr Effect Thermometry,"Spin-dependent charge transport in magnetic tunnel junctions (MTJs) can be | |
| manipulated by a temperature gradient, which can be utilized for spintronic and | |
| spin caloritronic applications. Evaluation of the thermally induced phenomena | |
| requires knowledge of the temperature differences across the oxide tunnel | |
| barrier adjacent to the ferromagnetic (FM) leads. However, it is challenging to | |
| accurately measure thermal properties of an oxide tunnel barrier consisting of | |
| only a few atomic layers. In this work, we experimentally interrogate the | |
| temperature evolutions in Ru/oxide/FM/seed/MgO (oxide=MgO, MgAl2O4; FM=Co, | |
| CoFeB; seed=Pt, Ta) structures having perpendicular magnetic anisotropy using | |
| ultrafast thermometry. The Ru layer is optically thick and heated by ultrafast | |
| laser pulses; the subsequent temperature changes are monitored using | |
| thermoreflectance of Ru and magneto-optic Kerr effect (MOKE) of the FM layers. | |
| We independently measure the response times of Co and CoFeB magnetism using | |
| quadratic MOKE and obtain {\tau}em=0.2 ps for Co and 2 ps for CoFeB. These time | |
| scales are much shorter than the time scale of heat transport through the oxide | |
| tunnel barrier, which occurs at 10-3000 ps. We determine effective thermal | |
| conductivities of MgO and MgAl2O4 tunnel barriers in the range of 0.4-0.6 W m-1 | |
| K-1, comparable to an estimate of the series conductance of the Ru/oxide and | |
| oxide/FM interfaces and an order of magnitude smaller than the thermal | |
| conductivity of MgO thin films. We find that the electron-phonon thermal | |
| conductance near the tunnel barrier is only a factor of 5-12 larger than the | |
| thermal conductance of the oxide tunnel barrier. Therefore, the drop in the | |
| electronic temperature is approximately 20-30% larger than the drop in the | |
| phonon temperature across the tunnel barrier.",1912.03588v1 | |
| 2021-06-18,Large perpendicular magnetic anisotropy in Ta/CoFeB/MgO on full coverage monolayer MoS2 and first principle study of its electronic structure,"Perpendicularly magnetized spin injector with high Curie temperature is a | |
| prerequisite for developing spin optoelectronic devices on 2D materials working | |
| at room temperature (RT) with zero applied magnetic field. Here, we report the | |
| growth of Ta/CoFeB/MgO structures with a large perpendicular magnetic | |
| anisotropy (PMA) on full coverage monolayer (ML) MoS2. A large perpendicular | |
| interface anisotropy energy of 0.975mJ/m2 has been obtained at the CoFeB/MgO | |
| interface, comparable to that observed in magnetic tunnel junction systems. It | |
| is found that the insertion of MgO between the ferromagnetic metal (FM) and the | |
| 2D material can effectively prevent the diffusion of the FM atoms into the 2D | |
| material. Moreover, the MoS2 ML favors a MgO(001) texture and plays a critical | |
| role to establish the large PMA. First principle calculations on a similar | |
| Fe/MgO/MoS2 structure reveal that the MgO thickness can modify the MoS2 band | |
| structure, from an indirect bandgap with 7ML-MgO to a direct bandgap with | |
| 3ML-MgO. Proximity effect induced by Fe results in a splitting of 10meV in the | |
| valence band at the {\Gamma} point for the 3ML-MgO structure while it is | |
| negligible for the 7ML-MgO structure. These results pave the way to develop RT | |
| spin optoelectronic devices on 2D transition-metal dichalcogenide materials.",2106.10317v1 | |
| 2022-10-20,Ultrafast behavior of induced and intrinsic magnetic moments in CoFeB/Pt bilayers probed by element-specific measurements in the extreme ultraviolet spectral range,"The ultrafast and element-specific response of magnetic systems containing | |
| ferromagnetic 3d transition metals and 4d/5d heavy metals is of interest both | |
| from a fundamental as well as an applied research perspective. However, to date | |
| no consensus about the main microscopic processes describing the interplay | |
| between intrinsic 3d and induced 4d/5d magnetic moments upon femtosecond laser | |
| excitation exist. In this work, we study the ultrafast response of CoFeB/Pt | |
| bilayers by probing element-specific, core-to-valence band transitions in the | |
| extreme ultraviolet spectral range using high harmonic radiation. We show that | |
| the combination of magnetic scattering simulations and analysis of the energy- | |
| and time-dependent magnetic asymmetries allows to accurately disentangle the | |
| element-specific response in spite of overlapping Co and Fe M$_{2,3}$ as well | |
| as Pt O$_{2,3}$ and N$_7$ resonances. We find a considerably smaller | |
| demagnetization time constant as well as much larger demagnetization amplitudes | |
| of the induced moment of Pt compared to the intrinsic moment of CoFeB. Our | |
| results are in agreement with enhanced spin-flip probabilities due to the high | |
| spin-orbit coupling localized at the heavy metal Pt, as well as with the | |
| recently formulated hypothesis that a laser generated, incoherent magnon | |
| population within the ferromagnetic film leads to an overproportional reduction | |
| of the induced magnetic moment of Pt.",2210.11390v3 | |
| 2009-08-17,The superferromagnetic state in the ensemble of oriented Stoner-Wohlfarth particles: a coercivity due to phase stability,"It is observed experimentally that the coercive field has an anomalous | |
| angular dependence at temperatures above the blocking temperature in physically | |
| nonpercolated granular films CoFeB-SiO$_{2}$ with anisotropic granules oriented | |
| in the same direction. It is shown that the anomaly is determined by the | |
| singularity of an angular dependence of the critical field causing the absolute | |
| loss of phase stability of the superferromagnetic state of an ensemble of | |
| interacting superparamagnetic granules.",0908.2286v1 | |
| 2014-04-04,Electrical detection of microwave assisted magnetization reversal by spin pumping,"Microwave assisted magnetization reversal has been investigated in a bilayer | |
| system of Pt/ferromagnet by detecting a change in the polarity of the spin | |
| pumping signal. The reversal process is studied in two material systems, | |
| Pt/CoFeB and Pt/NiFe, for different aspect ratios. The onset of the switching | |
| behavior is indicated by a sharp transition in the spin pumping voltage. At a | |
| threshold value of the external field, the switching process changes from | |
| partial to full reversal with increasing microwave power. The proposed method | |
| provides a simple way to detect microwave assisted magnetization reversal.",1404.1133v1 | |
| 2014-04-04,Thermally assisted domain wall nucleation in perpendicular anisotropy trilayer nanowires,"We study thermally assisted domain wall generation in perpendicular magnetic | |
| anisotropy CoFeB trilayer nanowires by the effect of Joule heating. The | |
| anomalous Hall effect is utilized to detect magnetization reversal in order to | |
| study the domain wall generation. We observe a statistical distribution in the | |
| switching process which is consistent with the thermal activation process. Our | |
| results show that the proposed method provides an efficient way for generating | |
| domain walls in perpendicular magnetic nanowires at predefined locations.",1404.1135v1 | |
| 2014-05-14,Generation of magnonic spin wave traps,"Spatially resolved measurements of the magnetization dynamics induced by an | |
| intense laser pump-pulse reveal that the frequencies of resulting spin wave | |
| modes depend strongly on the distance to the pump center. This can be | |
| attributed to a laser generated temperature profile. On a CoFeB thin film | |
| magnonic crystal, Damon-Eshbach modes are expected to propagate away from the | |
| point of excitation. The experiments show that this propagation is frustrated | |
| by the strong temperature gradient",1405.3470v1 | |
| 2017-01-06,Imaging magnetic vortex configurations in ferromagnetic nanotubes,"We image the remnant magnetization configurations of CoFeB and permalloy | |
| nanotubes (NTs) using x-ray magnetic circular dichroism photo-emission electron | |
| microscopy. The images provide direct evidence for flux-closure configurations, | |
| including a global vortex state, in which magnetization points | |
| circumferentially around the NT axis. Furthermore, micromagnetic simulations | |
| predict and measurements confirm that vortex states can be programmed as the | |
| equilibrium remnant magnetization configurations by reducing the NT aspect | |
| ratio.",1701.01685v1 | |
| 2021-03-31,Spin charge conversion in Rashba split ferromagnetic interfaces,"We show here theoretically and experimentally that a Rashba-split electron | |
| state inside a ferromagnet can efficiently convert a dynamical spin | |
| accumulation into an electrical voltage. The effect is understood to stem from | |
| the Rashba splitting but with a symmetry linked to the magnetization direction. | |
| It is experimentally measured by spin pumping in a CoFeB/MgO structure where it | |
| is found to be as efficient as the inverse spin Hall effect at play when Pt | |
| replaces MgO, with the extra advantage of not affecting the damping in the | |
| ferromagnet.",2103.16867v1 | |
| 2019-12-24,Large spin Hall angle and spin mixing conductance in highly resistive antiferromagnetic Mn2Au,"Antiferromagnetic (AFM) materials recently have shown interest in the | |
| research in spintronics due to its zero stray magnetic field, high anisotropy, | |
| and spin orbit coupling. In this context, the bi-metallic AFM Mn2Au has drawn | |
| attention because it exhibits unique properties and its Neel temperature is | |
| very high. Here, we report spin pumping and inverse spin Hall effect | |
| investigations in Mn2Au and CoFeB bilayer system using ferromagnetic resonance. | |
| We found large spin Hall angle {\theta}_SH = 0.22",1912.11522v2 | |
| 2008-09-20,Anomalous low-temperature magnetoelastic properties of nanogranular (CoFeB)$_{x}$-(SiO$_{2}$)$_{1-x}$,"We report magnetostatic measurements for granulated films | |
| (CoFeB)$_{x}$-(SiO$_{2}$)$_{1-x}$ with fabrication induced intraplanar | |
| anisotropy. The measurements have been performed in the film plane in the wide | |
| temperature interval 4.5$\div$300 K. They demonstrate that above films have | |
| low-temperature anomaly below the percolation threshold for conductivity. The | |
| essence of the above peculiarity is that below 100 K the temperature dependence | |
| of coercive field for magnetization along easy direction deviates strongly from | |
| Neel-Brown law. At temperature lowering, the sharp increase of coercivity is | |
| observed, accompanied by the appearance of coercive field for magnetization | |
| along hard direction in the film plane. We establish that observed effect is | |
| related to the properties of individual ferromagnetic granules. The effect | |
| weakens as granules merge into conglomerates at $x$ higher then percolation | |
| threshold and disappears completely at $x>1$. We explain the above effect as a | |
| consequence of the difference in thermal expansion coefficients of granule and | |
| cover material. At temperature lowering this difference weakens the envelopment | |
| of an individual granule by the cover matrix material, thus permitting to | |
| realize the spontaneous magnetostriction of a granule. The latter induces an | |
| additional anisotropy with new easy axis of a granule magnetization along the | |
| external magnetic field direction. Our explanation is tested and corroborated | |
| by the ferromagnetic resonance measurements in the films at $T$ = 300 K and $T$ | |
| = 77 K.",0809.3499v1 | |
| 2013-09-27,Structural and magnetic properties of Cr-diluted CoFeB,"The crystallization process and the magnetization of Cr diluted CoFeB was | |
| investigated in both ribbon samples and thin film samples with Cr content up to | |
| 30 at. %. A primary crystallization of bcc phase from an amorphous precursor in | |
| ribbon samples was observed when the annealing temperature rose to between 421 | |
| oC and 456 oC, followed by boron segregation at temperatures between 518 oC and | |
| 573 oC. The two onset crystallization temperatures showed strong dependences on | |
| both Cr and B concentrations. The impact of Cr concentration on the magnetic | |
| properties including a reduced saturation magnetization and an enhanced | |
| coercive field was also observed. The magnetizations of both ribbon samples and | |
| thin film samples were well fitted using the generalized Slater-Pauling curve | |
| with modified moments for B (-0.94 {\mu}B) and Cr (-3.6 {\mu}B). Possible | |
| origins of the enhanced coercive field were also discussed. We also achieved a | |
| damping parameter in CoFeCrB thin films at the same level as Co40Fe40B20, much | |
| lower than the value reported for CoFeCrB films previously. The results suggest | |
| a possible advantage of CoFeCrB in reducing the critical switching current | |
| density in Spin Transfer Torque Random Access Memory (STT-RAM).",1309.7331v1 | |
| 2014-01-15,Interface control of the magnetic chirality in CoFeB|MgO heterosctructures with heavy metal underlayers,"Recent advances in the understanding of spin orbital effects in ultrathin | |
| magnetic heterostructures have opened new paradigms to control magnetic moments | |
| electrically. The Dzyaloshinskii-Moriya interaction (DMI) is said to play a key | |
| role in forming a Neel-type domain wall that can be driven by the spin Hall | |
| torque, a torque resulting from the spin current generated in a neighboring | |
| non-magnetic layer via the spin Hall effect. Here we show that the strength and | |
| sign of the DMI can be changed by modifying the adjacent heavy metal underlayer | |
| (X) in perpendicularly magnetized X|CoFeB|MgO heterstructures. Albeit the same | |
| spin Hall angle, a domain wall moves along or against the electron flow | |
| depending on the underlayer. We find that the sense of rotation of a domain | |
| wall spiral11 is reversed when the underlayer is changed from Hf to W and the | |
| strength of DMI varies as the number of 5d electrons of the heavy metal layer | |
| changes. The DMI can even be tuned by adding nitrogen to the underlayer, thus | |
| allowing interface engineering of the magnetic texture in ultrathin magnetic | |
| heterostructures.",1401.3568v1 | |
| 2014-02-05,Fieldlike and antidamping spin-orbit torques in as-grown and annealed Ta/CoFeB/MgO layers,"We present a comprehensive study of the current-induced spin-orbit torques in | |
| perpendicularly magnetized Ta/CoFeB/MgO layers. The samples were annealed in | |
| steps up to 300 degrees C and characterized using x-ray absorption | |
| spectroscopy, transmission electron microscopy, resistivity, and Hall effect | |
| measurements. By performing adiabatic harmonic Hall voltage measurements, we | |
| show that the transverse (field-like) and longitudinal (antidamping-like) | |
| spin-orbit torques are composed of constant and magnetization-dependent | |
| contributions, both of which vary strongly with annealing. Such variations | |
| correlate with changes of the saturation magnetization and magnetic anisotropy | |
| and are assigned to chemical and structural modifications of the layers. The | |
| relative variation of the constant and anisotropic torque terms as a function | |
| of annealing temperature is opposite for the field-like and antidamping | |
| torques. Measurements of the switching probability using sub-{\mu}s current | |
| pulses show that the critical current increases with the magnetic anisotropy of | |
| the layers, whereas the switching efficiency, measured as the ratio of magnetic | |
| anisotropy energy and pulse energy, decreases. The optimal annealing | |
| temperature to achieve maximum magnetic anisotropy, saturation magnetization, | |
| and switching efficiency is determined to be between 240 degrees and 270 | |
| degrees C.",1402.0986v2 | |
| 2014-02-26,Anomalous temperature dependence of current induced torques in CoFeB|MgO heterostructures with Ta based underlayers,"We have studied the underlayer thickness and temperature dependences of the | |
| current induced effective field in CoFeB|MgO heterostructures with Ta based | |
| underlayers. The underlayer thickness at which the effective field saturates is | |
| found to be different between the two orthogonal components of the effective | |
| field, i.e. the damping-like term tends to saturate at smaller underlayer | |
| thickness than the field-like term. For large underlayer thickness films in | |
| which the effective field saturates, we find that the temperature significantly | |
| influences the size of the effective field. A striking difference is found in | |
| the temperature dependence of the two components: the damping-like term | |
| decreases whereas the field-like term increases with increasing temperature. | |
| Using a simple spin diffusion-spin transfer model, we find that all of these | |
| results can be accounted for provided the real and imaginary parts of an | |
| effective spin mixing conductance are negative. These results imply that either | |
| spin transport in this system is different from conventional metallic | |
| interfaces or effects other spin diffusion into the magnetic layer need to be | |
| taken account in order to model the system accurately.",1402.6388v1 | |
| 2014-10-28,Current driven asymmetric magnetization switching in perpendicularly magnetized CoFeB/MgO heterostructures,"The flow of in-plane current through ultrathin magnetic heterostructures can | |
| cause magnetization switching or domain wall nucleation owing to bulk and | |
| interfacial effects. Within the magnetic layer, the current can create magnetic | |
| instabilities via spin transfer torques (STT). At interface(s), spin current | |
| generated from the spin Hall effect in a neighboring layer can exert torques, | |
| referred to as the spin Hall torques, on the magnetic moments. Here, we study | |
| current induced magnetization switching in perpendicularly magnetized CoFeB/MgO | |
| heterostructures with a heavy metal (HM) underlayer. Depending on the thickness | |
| of the HM underlayer, we find distinct differences in the inplane field | |
| dependence of the threshold switching current. The STT is likely responsible | |
| for the magnetization reversal for the thinner underlayer films whereas the | |
| spin Hall torques cause the switching for thicker underlayer films. For the | |
| latter, we find differences in the switching current for positive and negative | |
| currents and initial magnetization directions. We find that the growth process | |
| during the film deposition introduces an anisotropy that breaks the symmetry of | |
| the system and causes the asymmetric switching. The presence of such symmetry | |
| breaking anisotropy enables deterministic magnetization switching at zero | |
| external fields.",1410.7473v2 | |
| 2015-06-12,Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures,"Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts | |
| extensive attentions due to its non-volatility, high density and low power | |
| consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel | |
| junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well | |
| as a large value of perpendicular magnetic anisotropy (PMA). It has been | |
| experimentally proven that a capping layer coating on CoFeB layer is essential | |
| to obtain a strong PMA. However, the physical mechanism of such effect remains | |
| unclear. In this paper, we investigate the origin of the PMA in | |
| MgO/CoFe/metallic capping layer structures by using a first-principles | |
| computation scheme. The trend of PMA variation with different capping materials | |
| agrees well with experimental results. We find that interfacial PMA in the | |
| three-layer structures comes from both the MgO/CoFe and CoFe/capping layer | |
| interfaces, which can be analyzed separately. Furthermore, the PMAs in the | |
| CoFe/capping layer interfaces are analyzed through resolving the magnetic | |
| anisotropy energy by layer and orbital. The variation of PMA with different | |
| capping materials is attributed to the different hybridizations of both d and p | |
| orbitals via spin-orbital coupling. This work can significantly benefit the | |
| research and development of nanoscale STT-MRAM.",1506.04078v4 | |
| 2016-05-07,Giant interfacial perpendicular magnetic anisotropy in MgO/CoFe/capping layer structures,"Magnetic tunnel junction (MTJ) based on CoFeB/MgO/CoFeB structures is of | |
| great interest due to its application in the spin-transfer-torque magnetic | |
| random access memory (STT-MRAM). Large interfacial perpendicular magnetic | |
| anisotropy (PMA) is required to achieve high thermal stability. Here we use | |
| first-principles calculations to investigate the magnetic anisotropy energy | |
| (MAE) of MgO/CoFe/capping layer structures, where the capping materials include | |
| 5d metals Hf, Ta, Re, Os, Ir, Pt, Au and 6p metals Tl, Pb, Bi. We demonstrate | |
| that it is feasible to enhance PMA by using proper capping materials. | |
| Relatively large PMA is found in the structures with capping materials of Hf, | |
| Ta, Os, Ir and Pb. More importantly, the MgO/CoFe/Bi structure gives rise to | |
| giant PMA (6.09 mJ/m2), which is about three times larger than that of the | |
| MgO/CoFe/Ta structure. The origin of the MAE is elucidated by examining the | |
| contributions to MAE from each atomic layer and orbital. These findings provide | |
| a comprehensive understanding of the PMA and point towards the possibility to | |
| achieve advanced-node STT-MRAM with high thermal stability.",1605.02247v5 | |
| 2017-08-14,Current-induced magnetization switching in atom-thick tungsten engineered perpendicular magnetic tunnel junctions with large tunnel magnetoresistance,"Perpendicular magnetic tunnel junctions based on MgO/CoFeB structures are of | |
| particular interest for magnetic random-access memories because of their | |
| excellent thermal stability, scaling potential, and power dissipation. However, | |
| the major challenge of current-induced switching in the nanopillars with both a | |
| large tunnel magnetoresistance ratio and a low junction resistance is still to | |
| be met. Here, we report spin transfer torque switching in nano-scale | |
| perpendicular magnetic tunnel junctions with a magnetoresistance ratio up to | |
| 249% and a resistance area product as low as 7.0 {\Omega}.{\mu}m2, which | |
| consists of atom-thick W layers and double MgO/CoFeB interfaces. The efficient | |
| resonant tunnelling transmission induced by the atom-thick W layers could | |
| contribute to the larger magnetoresistance ratio than conventional structures | |
| with Ta layers, in addition to the robustness of W layers against high | |
| temperature diffusion during annealing. The switching critical current density | |
| could be lower than 3.0 MA.cm-2 for devices with a 45 nm radius.",1708.04111v3 | |
| 2018-01-11,Efficient Charge-Spin Conversion and Magnetization Switching though Rashba Effect at Topological Insulator/Ag Interface,"We report the observation of efficient charge-to-spin conversion in the | |
| three-dimensional topological insulator (TI) Bi2Se3 and Ag bilayer by the | |
| spin-torque ferromagnetic resonance technique. The spin orbit torque ratio in | |
| the Bi2Se3/Ag/CoFeB heterostructure shows a significant enhancement as the Ag | |
| thickness increases to ~2 nm and reaches a value of 0.5 for 5 nm Ag, which is | |
| ~3 times higher than that of Bi2Se3/CoFeB at room temperature. The observation | |
| reveals the interfacial effect of Bi2Se3/Ag exceeds that of the topological | |
| surface states (TSS) in the Bi2Se3 layer and plays a dominant role in the | |
| charge-to-spin conversion in the Bi2Se3/Ag/CoFeB system. Based on the | |
| first-principles calculations, we attribute our observation to the large | |
| Rashba-splitting bands which wrap the TSS band and has the same net spin | |
| polarization direction as TSS of Bi2Se3. Subsequently, we demonstrate for the | |
| first time the Rashba induced magnetization switching in Bi2Se3/Ag/Py with a | |
| low current density of 5.8 X 10^5 A/cm2.",1801.03689v1 | |
| 2020-01-13,Large and Robust Charge-to-Spin Conversion in Sputtered Conductive WTex with Disorder,"Topological materials with large spin-orbit coupling and immunity to | |
| disorder-induced symmetry breaking show great promise for efficiently | |
| converting charge to spin. Here, we report that long-range disordered sputtered | |
| WTex thin films exhibit local chemical and structural order as those of Weyl | |
| semimetal WTe2 and conduction behavior that is consistent with semi-metallic | |
| Weyl fermion. We find large charge-to-spin conversion properties and electrical | |
| conductivity in thermally annealed sputtered WTex films that are comparable | |
| with those in crystalline WTe2 flakes. Besides, the strength of unidirectional | |
| spin Hall magnetoresistance in annealed WTex/Mo/CoFeB heterostructure is 5 to | |
| 20 times larger than typical SOT layer/ferromagnet heterostructures reported at | |
| room temperature. We further demonstrate room temperature damping-like | |
| SOT-driven magnetization switching of in-plane magnetized CoFeB. These large | |
| charge-to-spin conversion properties that are robust in the presence of | |
| long-range disorder and thermal annealing pave the way for industrial | |
| application of a new class of sputtered semimetals.",2001.04054v2 | |
| 2021-07-16,Large Unidirectional Magnetoresistance in Metallic Heterostructures in the Spin Transfer Torque Regime,"A large unidirectional magnetoresistance (UMR) ratio of UMR/$R_{xx}\sim$ | |
| $0.36\%$ is found in W/CoFeB metallic bilayer heterostructures at room | |
| temperature. Three different regimes in terms of the current dependence of UMR | |
| ratio are identified: A spin-dependent-scattering mechanism regime at small | |
| current densities $J \sim$ $10$$^{9}$A/m$^{2}$ (UMR ratio $\propto$ $J$), a | |
| spin-magnon-interaction mechanism regime at intermediate $J \sim$ | |
| $10$$^{10}$A/m$^{2}$ (UMR ratio $\propto$ $J$$^{3}$), and a spin-transfer | |
| torque (STT) regime at $J \sim$ $10$$^{11}$A/m$^{2}$ (UMR ratio independent of | |
| $J$). We verify the direct correlation between this large UMR and the transfer | |
| of spin angular momentum from the W layer to the CoFeB layer by both | |
| field-dependent and current-dependent UMR characterizations. Numerical | |
| simulations further confirm that the large STT-UMR stems from the tilting of | |
| the magnetization affected by the spin Hall effect-induced spin-transfer | |
| torques. An alternative approach to estimate damping-like spin-torque | |
| efficiencies from magnetic heterostructures is also proposed.",2107.07780v1 | |
| 2017-05-18,Magnetization dynamics and its scattering mechanism in thin CoFeB films with interfacial anisotropy,"Studies of magnetization dynamics have incessantly facilitated the discovery | |
| of fundamentally novel physical phenomena, making steady headway in the | |
| development of magnetic and spintronics devices. The dynamics can be induced | |
| and detected electrically, offering new functionalities in advanced electronics | |
| at the nanoscale. However, its scattering mechanism is still disputed. | |
| Understanding the mechanism in thin films is especially important, because most | |
| spintronics devices are made from stacks of multilayers with nanometer | |
| thickness. The stacks are known to possess interfacial magnetic anisotropy, a | |
| central property for applications, whose influence on the dynamics remains | |
| unknown. Here, we investigate the impact of interfacial anisotropy by adopting | |
| CoFeB/MgO as a model system. Through systematic and complementary measurements | |
| of ferromagnetic resonance (FMR), on a series of thin films, we identify | |
| narrower FMR linewidths at higher temperatures. We explicitly rule out the | |
| temperature dependence of intrinsic damping as a possible cause, and it is also | |
| not expected from existing extrinsic scattering mechanisms for ferromagnets. We | |
| ascribe this observation to motional narrowing, an old concept so far neglected | |
| in the analyses of FMR spectra. The effect is confirmed to originate from | |
| interfacial anisotropy, impacting the practical technology of spin-based | |
| nanodevices up to room temperature.",1705.06624v1 | |
| 2019-01-26,Low spin-polarization in the heavy metal\ferromagnet structures detected through the domain wall motion by synchronized magnetic field and current,"CoFeB is a very soft material, in which Domain Wall (DW) can be moved easily | |
| under a weak magnetic field. However, it is very difficult to move DWs in | |
| Ta\CoFeB\MgO nanowires with interfacial perpendicular magnetic anisotropy | |
| through a spin-polarized current, and this limits the perspectives of racetrack | |
| memory driven by the current-in-plane mechanism. To investigate this | |
| phenomenon, we performed experiments of DW velocity measurement by applying a | |
| magnetic field and a current simultaneously. Working in the precessional | |
| regime, we have been able to see a very important effect of the spin-polarized | |
| current, which allows evaluating the polarization rate of the charge carriers. | |
| An unexpected quite low spin polarization rate down to 0.26 have been obtained, | |
| which can explain the low efficiency of DW motion induced by the spin-polarized | |
| current. Possible reasons for this low rate are analyzed, such as the spin | |
| relaxation in the Ta layer.",1901.09256v1 | |
| 2018-12-06,Optimization of high performance spintronic terahertz sources,"To achieve high efficiency and good performance of spintronic terahertz | |
| sources, we propose and corroborate a remnant magnetization method to radiate | |
| continuously and stably terahertz pulses from W/CoFeB/Pt magnetic nanofilms | |
| without carrying magnets on the transmitters driven by femtosecond laser | |
| pulses. We systematically investigate the influences of the pumping central | |
| wavelength and find out the optimal wavelength for a fixed sample thickness. We | |
| also optimize the incidence angle of the pumping laser and find the emission | |
| efficiency is enhanced under oblique incidence. Combing the aforementioned | |
| optimizations, we finally obtain comparable radiation efficiency and broadband | |
| spectra in W/CoFeB/Pt heterostructures compared with that from 1 mm thick ZnTe | |
| nonlinear crystals via optical rectification under the same pumping conditions | |
| of 100 fs pulse duration from a Ti:sapphire laser oscillator, which was not | |
| previously demonstrated under such pulse duration. We believe our observations | |
| not only benefit for a deep insight into the physics of femtosecond spin | |
| dynamics, but also help develop novel and cost-effective ultrabroadband | |
| spintronic terahertz emitters.",1812.02286v2 | |
| 2020-08-04,Ultrathin perpendicular free layers for lowering the switching current in STT-MRAM,"The critical current density $J_{c0}$ required for switching the | |
| magnetization of the free layer (FL) in a spin-transfer torque magnetic random | |
| access memory (STT-MRAM) cell is proportional to the product of the damping | |
| parameter, saturation magnetization and thickness of the free layer, $\alpha | |
| M_S t_F$. Conventional FLs have the structure CoFeB/nonmagnetic spacer/CoFeB. | |
| By reducing the spacer thickness, W in our case, and also splitting the single | |
| W layer into two layers of sub-monolayer thickness, we have reduced $t_F$ while | |
| minimizing $\alpha$ and maximizing $M_S$, ultimately leading to lower $J_{c0}$ | |
| while maintaining high thermal stability. Bottom-pinned MRAM cells with device | |
| diameter in the range of 55-130 nm were fabricated, and $J_{c0}$ is lowest for | |
| the thinnest (1.2 nm) FLs, down to 4 MA/cm$^2$ for 65 nm devices, $\sim$30% | |
| lower than 1.7 nm FLs. The thermal stability factor $\Delta_{\mathrm{dw}}$, as | |
| high as 150 for the smallest device size, was determined using a domain wall | |
| reversal model from field switching probability measurements. With high | |
| $\Delta_{\mathrm{dw}}$ and lowest $J_{c0}$, the thinnest FLs have the highest | |
| spin-transfer torque efficiency.",2008.01343v1 | |
| 2021-03-08,Anisotropic magnon-magnon coupling in synthetic antiferromagnets,"The magnon-magnon coupling in synthetic antiferromagnets advances it as | |
| hybrid magnonic systems to explore the quantum information technologies. To | |
| induce the magnon-magnon coupling, the parity symmetry between two | |
| magnetization needs to be broken. Here we experimentally demonstrate a | |
| convenient method to break the parity symmetry by the asymmetric thickness of | |
| two magnetic layers and thus introduce a magnon-magnon coupling in Ir-based | |
| synthetic antiferromagnets CoFeB(10 nm)/Ir(tIr=0.6 nm, 1.2 nm)/CoFeB(13 nm). | |
| Remarkably, we find that the weakly uniaxial anisotropy field (~ 20 Oe) makes | |
| the magnon-magnon coupling anisotropic. The coupling strength presented by a | |
| characteristic anticrossing gap varies in the range between 0.54 GHz and 0.90 | |
| GHz for tIr =0.6 nm, and between nearly zero to 1.4 GHz for tIr = 1.2 nm, | |
| respectively. Our results demonstrate a feasible way to induce the | |
| magnon-magnon coupling by an asymmetric structure and tune the coupling | |
| strength by varying the direction of in-plane magnetic field. The magnon-magnon | |
| coupling in this highly tunable material system could open exciting | |
| perspectives for exploring quantum-mechanical coupling phenomena.",2103.04512v2 | |
| 2017-02-01,Continuous Tuning the Magnitude and Direction of Spin-Orbit Torque Using Bilayer Heavy Metals,"Spin-orbit torques (SOTs) have opened a new path to switch the magnetization | |
| in perpendicularly magnetized films and are of great interest due to their | |
| potential applications in novel data storage technology, such as the magnetic | |
| random access memory (MRAM). The effective manipulation of SOT has thus become | |
| an important step towards these applications. Here, current induced spin-orbit | |
| effective fields and magnetization switching are investigated in | |
| Pt/Ta/CoFeB/MgO structures with bilayer heavy metals. With a fixed thickness (1 | |
| nm) of the Ta layer, the magnitude and sign of current induced spin-orbit | |
| effective fields can be continuously tuned by changing the Pt layer thickness, | |
| consistent with the current induced magnetization switching data. The ratio of | |
| longitudinal to transverse spin-orbit effective fields is found to be | |
| determined by the Ta/CoFeB interface and can be continuously tuned by changing | |
| the Pt layer thickness. The Dzyaloshinskii-Moriya interaction (DMI) is found to | |
| be weak and shows an insignificant variation with the Pt thickness. The results | |
| demonstrate an effective method to tune SOTs utilizing bilayer heavy metals | |
| without affecting the DMI, a desirable feature which will be useful for the | |
| design of SOT-based devices.",1702.00147v1 | |
| 2017-06-19,Investigation of the Dzyaloshinskii-Moriya interaction and room temperature skyrmions in W/CoFeB/MgO thin films and microwires,"Recent studies have shown that material structures, which lack structural | |
| inversion symmetry and have high spin-orbit coupling can exhibit chiral | |
| magnetic textures and skyrmions which could be a key component for next | |
| generation storage devices. The Dzyaloshinskii-Moriya Interaction (DMI) that | |
| stabilizes skyrmions is an anti-symmetric exchange interaction favoring | |
| non-collinear orientation of neighboring spins. It has been shown that material | |
| systems with high DMI can lead to very efficient domain wall and skyrmion | |
| motion by spin-orbit torques. To engineer such devices, it is important to | |
| quantify the DMI for a given material system. Here we extract the DMI at the | |
| Heavy Metal (HM) /Ferromagnet (FM) interface using two complementary | |
| measurement schemes namely asymmetric domain wall motion and the magnetic | |
| stripe annihilation. By using the two different measurement schemes, we find | |
| for W(5 nm)/Co20Fe60B20(0.6 nm)/MgO(2 nm) the DMI to be 0.68 +/- 0.05 mJ/m2 and | |
| 0.73 +/- 0.5 mJ/m2, respectively. Furthermore, we show that this DMI stabilizes | |
| skyrmions at room temperature and that there is a strong dependence of the DMI | |
| on the relative composition of the CoFeB alloy. Finally we optimize the layers | |
| and the interfaces using different growth conditions and demonstrate that a | |
| higher deposition rate leads to a more uniform film with reduced pinning and | |
| skyrmions that can be manipulated by Spin-Orbit Torques.",1706.05987v1 | |
| 2018-04-30,Field-Free Switching of Perpendicular Magnetic Tunnel Junction via Voltage-Gated Spin Hall Effect for Low-Power Spintronic Memory,"Spin Hall effect (SHE) and voltage-controlled magnetic anisotropy (VCMA) are | |
| two promising methods for low-power electrical manipulation of magnetization. | |
| Recently, magnetic field-free switching of perpendicular magnetization through | |
| SHE has been reported with the aid of an exchange bias from an | |
| antiferromagnetic IrMn layer. In this letter, we experimentally demonstrate | |
| that the IrMn/CoFeB/MgO structure exhibits a VCMA effect of 39 fJ/Vm, which is | |
| comparable to that of the Ta/CoFeB/MgO structure. Magnetization dynamics under | |
| a combination of the SHE and VCMA are modeled and simulated. It is found that, | |
| by applying a voltage of 1.5 V, the critical SHE switching current can be | |
| decreased by 10 times owing to the VCMA effect, leading to low-power | |
| operations. Furthermore, a high-density spintronic memory structure can be | |
| built with multiple magnetic tunnel junctions (MTJs) located on a single IrMn | |
| strip. Through hybrid CMOS/MTJ simulations, we demonstrate that fast-speed | |
| write operations can be achieved with power consumption of only 8.5 fJ/bit. | |
| These findings reveal the possibility to realize high-density and low-power | |
| spintronic memory manipulated by voltage-gated SHE.",1804.11025v1 | |
| 2020-06-04,Defect-Correlated Skyrmions and Controllable Generation in Perpendicularly Magnetized CoFeB Ultrathin Films,"Skyrmions have attracted significant interest due to their topological spin | |
| structures and fascinating physical features. The skyrmion phase arises in | |
| materials with Dzyaloshinskii-Moriya (DM) interaction at interfaces or in | |
| volume of non-centrosymmetric materials. However, although skyrmions were | |
| generated experimentally, one critical intrinsic relationship between | |
| fabrication, microstructures, magnetization and the existence of skyrmions | |
| remains to be established. Here, two series of CoFeB ultrathin films with | |
| controlled atomic scale structures are employed to reveal this relationship. By | |
| inverting the growth order, the amount of defects can be artificially tuned, | |
| and skyrmions are shown to be preferentially formed at defect sites. The stable | |
| region and the density of the skyrmions can be efficiently controlled in the | |
| return magnetization loops by utilizing first-order reversal curves to reach | |
| various metastable states. These findings establish the general and intrinsic | |
| relationship from sample preparation to skyrmion generation, offering an | |
| universal method to control skyrmion density.",2006.02864v1 | |
| 2020-07-27,Magnonic band structure in vertical meander-shaped CoFeB thin films,"The dispersion of spin waves in vertical meander-shaped CoFeB thin films | |
| consisting of segments located at 90{\deg} angles with respect to each other is | |
| investigated by Brillouin light scattering spectroscopy. We reveal the periodic | |
| character of several dispersive branches as well as alternating frequency | |
| ranges where spin waves are allowed or forbidden to propagate. Noteworthy is | |
| the presence of the frequency band gaps between each couple of successive modes | |
| only for wave numbers k=n$\pi$/a, where n is an even integer number and a is | |
| the size of the meander unit cell, whereas the spectra show propagating modes | |
| in the orthogonal film segments for the other wavenumbers. The micromagnetic | |
| simulations and analytical calculations allow us to understand and explain the | |
| results in terms of the mode spatial localization and symmetry. The obtained | |
| results demonstrate the wave propagation in three dimensions opening the path | |
| for multi-level magnonic architectures for signal processing.",2007.13707v2 | |
| 2020-09-14,Memristive control of mutual SHNO synchronization for neuromorphic computing,"Synchronization of large spin Hall nano-oscillators (SHNO) arrays is an | |
| appealing approach toward ultra-fast non-conventional computing based on | |
| nanoscale coupled oscillator networks. However, for large arrays, interfacing | |
| to the network, tuning its individual oscillators, their coupling, and | |
| providing built-in memory units for training purposes, remain substantial | |
| challenges. Here, we address all these challenges using memristive gating of | |
| W/CoFeB/MgO/AlOx based SHNOs. In its high resistance state (HRS), the memristor | |
| modulates the perpendicular magnetic anisotropy (PMA) at the CoFeB/MgO | |
| interface purely by the applied electric field. In its low resistance state | |
| (LRS), and depending on the voltage polarity, the memristor adds/subtracts | |
| current to/from the SHNO drive. The operation in both the HRS and LRS affects | |
| the SHNO auto-oscillation mode and frequency, which can be tuned up to 28 | |
| MHz/V. This tuning allows us to reversibly turn on/off mutual synchronization | |
| in chains of four SHNOs. We also demonstrate two individually controlled | |
| memristors to tailor both the coupling strength and the frequency of the | |
| synchronized state. Memristor gating is therefore an efficient approach to | |
| input, tune, and store the state of the SHNO array for any non-conventional | |
| computing paradigm, all in one platform.",2009.06594v1 | |
| 2021-02-15,Controlling Domain-Wall Nucleation in Ta/CoFeB/MgO Nanomagnets via Local Ga+ Ion Irradiation,"Comprehensive control of the domain wall nucleation process is crucial for | |
| spin-based emerging technologies ranging from random-access and storage-class | |
| memories over domain-wall logic concepts to nanomagnetic logic. In this work, | |
| focused Ga+ ion-irradiation is investigated as an effective means to control | |
| domain-wall nucleation in Ta/CoFeB/MgO nanostructures. We show that analogously | |
| to He+ irradiation, it is not only possible to reduce the perpendicular | |
| magnetic anisotropy but also to increase it significantly, enabling new, | |
| bidirectional manipulation schemes. First, the irradiation effects are assessed | |
| on film level, sketching an overview of the dose-dependent changes in the | |
| magnetic energy landscape. Subsequent time-domain nucleation characteristics of | |
| irradiated nanostructures reveal substantial increases in the anisotropy fields | |
| but surprisingly small effects on the measured energy barriers, indicating | |
| shrinking nucleation volumes. Spatial control of the domain wall nucleation | |
| point is achieved by employing focused irradiation of pre-irradiated magnets, | |
| with the diameter of the introduced circular defect controlling the coercivity. | |
| Special attention is given to the nucleation mechanisms, changing from a | |
| Stoner-Wohlfarth particle's coherent rotation to depinning from an anisotropy | |
| gradient. Dynamic micromagnetic simulations and related measurements are used | |
| in addition to model and analyze this depinning-dominated magnetization | |
| reversal.",2102.07540v1 | |
| 2021-06-12,Spin pumping and inverse spin Hall effect in CoFeB/C$_{60}$ bilayers,"Pure spin current based research is mostly focused on ferromagnet (FM)/heavy | |
| metal (HM) system. Because of the high spin orbit coupling (SOC) these HMs | |
| exhibit short spin diffusion length and therefore possess challenges for device | |
| application. Low SOC (elements of light weight) and large spin diffusion length | |
| make the organic semiconductors (OSCs) suitable for future spintronic | |
| applications. From theoretical model it is explained that, due to $\pi$ - | |
| $\sigma$ hybridization the curvature of the C$_{60}$ molecules may increase the | |
| SOC strength. Here, we have investigated spin pumping and inverse spin hall | |
| effect (ISHE) in CoFeB/C$_{60}$ bilayer system using coplanar wave guide based | |
| ferromagnetic resonance (CPW-FMR) set-up. We have performed angle dependent | |
| ISHE measurement to disentangle the spin rectification effects for example | |
| anisotropic magnetoresistance, anomalous Hall effect etc. Further, effective | |
| spin mixing conductance (g$_{eff}^{\uparrow\downarrow}$) and spin Hall angle | |
| ($\theta_{SH}$) for C$_{60}$ have been reported here. The evaluated value for | |
| $\theta_{SH}$ is 0.055.",2106.06829v2 | |
| 2022-06-29,Tailoring the switching efficiency of magnetic tunnel junctions by the fieldlike spin-orbit torque,"Current-induced spin-orbit torques provide a versatile tool for switching | |
| magnetic devices. In perpendicular magnets, the dampinglike component of the | |
| torque is the main driver of magnetization reversal. The degree to which the | |
| fieldlike torque assists the switching is a matter of debate. Here we study the | |
| switching of magnetic tunnel junctions with a CoFeB free layer and either W or | |
| Ta underlayers, which have a ratio of fieldlike to dampinglike torque of 0.3 | |
| and 1, respectively. We show that the fieldlike torque can either assist or | |
| hinder the switching of CoFeB when the static in-plane magnetic field required | |
| to define the polarity of spin-orbit torque switching has a component | |
| transverse to the current. In particular, the non-collinear alignment of the | |
| field and current can be exploited to increase the switching efficiency and | |
| reliability compared to the standard collinear alignment. By probing individual | |
| switching events in real-time, we also show that the combination of transverse | |
| magnetic field and fieldlike torque can accelerate or decelerate the reversal | |
| onset. We validate our observations using micromagnetic simulations and | |
| extrapolate the results to materials with different torque ratios. Finally, we | |
| propose device geometries that leverage the fieldlike torque for density | |
| increase in memory applications and synaptic weight generation.",2206.14587v2 | |
| 2022-08-17,Magnetic domain scanning imaging using phase-sensitive THz-pulse detection,"In our study, we determine the alignment of magnetic domains in a CoFeB layer | |
| using THz radiation. We generate THz-pulses by fs-laser-pulses in magnetized | |
| CoFeB/Pt heterostructures, based on spin currents. An LT-GaAs Auston switch | |
| detects the radiation phase-sensitively and allows to determine the | |
| magnetization alignment. Our scanning technique with motorized stages with step | |
| sizes in the sub-micrometer range, allows to image two dimensional magnetic | |
| structures. Theoretically the resolution is restricted to half of the | |
| wavelength if focusing optics in the far-field limit are used. By applying | |
| near-field imaging, the spatial resolution is enhanced to the single digit | |
| micrometer range. For this purpose, spintronic emitters in diverse geometric | |
| shapes, e.g. circles, triangles, squares, and sizes are prepared to observe the | |
| formation of magnetization patterns. The alignment of the emitted THz radiation | |
| can be influenced by applying unidirectional external magnetic fields. We | |
| demonstrate how magnetic domains with opposite alignment and different shapes | |
| divided by domain walls are created by demagnetizing the patterns using minor | |
| loops and imaged using phase sensitive THz radiation detection. For analysis, | |
| the data is compared to Kerr microscope images. The possibility to combine this | |
| method with THz range spectroscopic information of magnetic texture or | |
| antiferromagnets in direct vicinity to the spintronic emitter, makes this | |
| detection method interesting for much wider applications probing THz excitation | |
| in spin systems with high resolution beyond the Abbe diffraction limit, limited | |
| solely by the laser excitation area.",2208.08219v1 | |
| 2022-08-19,Revealing nanoscale disorder in W/CoFeB/MgO ultra-thin films using domain wall motion,"Disorder in ultra-thin magnetic films can significantly hinder domain wall | |
| motion. One of the main issues on the path towards efficient domain wall based | |
| devices remains the characterization of the pinning landscape at the nanoscale. | |
| In this paper, we study domain wall motion in W/CoFeB/MgO thin films with | |
| perpendicular magnetic anisotropy crystallized by annealing at 400$^{\circ}$C | |
| and a process based on He$^{+}$ irradiation combined with elevated | |
| temperatures. Magnetic properties are similar for the whole series of samples, | |
| while the magnetic domain wall mobility is critically improved in the | |
| irradiated samples. By using an analytical model to extract nanoscale pinning | |
| parameters, we reveal important variations in the disorder of the crystallized | |
| samples. This work offers a unique opportunity to selectively analyze the | |
| effects of disorder on the domain wall dynamics, without the contribution of | |
| changes in the magnetic properties. Our results highlight the importance of | |
| evaluating the nanoscale pinning parameters of the material when designing | |
| devices based on domain wall motion, which in return can be a powerful tool to | |
| probe the disorder in ultra-thin magnetic films.",2208.09280v1 | |
| 2022-09-05,Nonlocal detection of interlayer three-magnon coupling,"A leading nonlinear effect in magnonics is the interaction that splits a | |
| high-frequency magnon into two low-frequency ones with conserved linear | |
| momentum. Here, we report experimental observation of nonlocal three-magnon | |
| scattering between spatially separated magnetic systems, viz. a CoFeB nanowire | |
| and an yttrium iron garnet (YIG) thin film. Above a certain threshold power of | |
| an applied microwave field, a CoFeB Kittel magnon splits into a pair of | |
| counter-propagating YIG magnons that induce voltage signals in Pt electrodes on | |
| each side, in excellent agreement with model calculations based on the | |
| interlayer dipolar interaction. The excited YIG magnon pairs reside mainly in | |
| the first excited (n=1) perpdendicular standing spin-wave mode. With increasing | |
| power, the n=1 magnons successively scatter into nodeless (n=0) magnons through | |
| a four-magnon process. Our results help to assess non-local scattering | |
| processes in magnonic circuits that may enable quantum entanglement between | |
| distant magnons for quantum information applications.",2209.01875v1 | |
| 2022-10-04,Strain Coupled Domains in BaTiO3(111)-CoFeB Heterostructures,"Domain pattern transfer from ferroelectric to ferromagnetic materials is a | |
| critical step for the electric field control of magnetism and has the potential | |
| to provide new schemes for low-power data storage and computing devices. Here | |
| we investigate domain coupling in BaTiO$_3$(111)/CoFeB heterostructures by | |
| direct imaging in a wide-field Kerr microscope. The magnetic easy axis is found | |
| to locally change direction as a result of the underlying ferroelectric domains | |
| and their polarisation. By plotting the remanent magnetisation as a function of | |
| angle in the plane of the CoFeB layer, we find that the magnetic easy axes in | |
| adjacent domains are angled at 60$^\circ$ or 120$^\circ$, corresponding to the | |
| angle of rotation of the polarisation from one ferroelectric domain to the | |
| next, and that the magnetic domain walls may be charged or uncharged depending | |
| on the magnetic field history. Micromagnetic simulations show that the | |
| properties of the domain walls vary depending on the magnetoelastic easy axis | |
| configuration and the charged or uncharged nature of the wall. The | |
| configuration where the easy axis alternates by 60$^\circ$ and a charged wall | |
| is initialised exhibits the largest change in domain wall width from 192 nm to | |
| 119 nm as a function of in-plane magnetic field. Domain wall width tuning | |
| provides an additional degree of freedom for devices that seek to manipulate | |
| magnetic domain walls using strain coupling to ferroelectrics.",2210.01511v1 | |
| 2023-03-10,Field-driven collapsing dynamics of skyrmions in magnetic multilayers,"Magnetic skyrmions are fascinating topological particle-like textures | |
| promoted by a trade-off among interfacial properties (perpendicular anisotropy | |
| and Dzyaloshinskii-Moriya interaction (DMI)) and dipolar interactions. | |
| Depending on the dominant interaction, complex spin textures, including pure | |
| N\'eel and hybrid skyrmions have been observed in multilayer heterostructures. | |
| A quantification of these different spin textures typically requires a | |
| depth-reoslved magnetic imaging or scattering techniques. In the present work, | |
| we will show qualitatively different collapsing dynamics for pure N\'eel and | |
| hybrid skyrmions induced by a perpendicular magnetic field in two | |
| representative systems, [Pt/Co/Ir]15 and [Ta/CoFeB/MgO]15 multilayers. | |
| Skyrmions in the former stack undergo two morphological transitions, upon | |
| reversing the perpendicular field direction. Skyrmions in [Ta/CoFeB/MgO]15 | |
| multilayers exhibit a continuous transition, which is mainly linked to a | |
| reversible change of the skyrmion size. A full micromagnetic phase diagram is | |
| presented to identify these two collapsing mechanisms as a function of material | |
| parameters. Since the two distinct collapsing dynamics rely on the detailed | |
| layer-dependent spin structures of skyrmions, they could be used as potential | |
| fingerprints for identifying the skyrmion type in magnetic multilayers. Our | |
| work suggests the employment of pure and hybrid skyrmions for specific | |
| applications, due to the strong correlation between the skyrmion dynamics and | |
| 3-dimentional spin profiles.",2303.05988v1 | |
| 2023-07-05,Comparative Analysis of THz Signal Emission from SiO$_2$/CoFeB/Metal Heterostructures: Wideband and High-Frequency THz Signal Advantage of PtBi-based Emitter,"Spintronic THz emitters have attracted much attention due to their desirable | |
| properties, such as affordability, ultra-wideband capability, high efficiency, | |
| and tunable polarization. In this study, we investigate the characteristics of | |
| THz signals, including their frequency, bandwidth, and amplitude, emitted from | |
| a series of heterostructures with ferromagnetic (FM) and nonmagnetic (NM) | |
| materials. The FM layer consists of a wedge-shaped CoFeB layer with a thickness | |
| of 0 to 5 nm, while the NM materials include various metals such as Pt, Au, W, | |
| Ru, Pt$_{\%92}$Bi$_{\%8}$, and Ag$_{\%90}$Bi$_{\%10}$ alloys. Our experiments | |
| show that the emitter with Pt-NM layer has the highest amplitude of the emitted | |
| THz signal. However, the PtBi-based emitter exhibits a higher central THz peak | |
| and wider bandwidth, making it a promising candidate for broadband THz | |
| emitters. These results pave the way for further exploration of the specific | |
| compositions of Pt$_{1-x}$Bi$_{x}$ for THz emitter design, especially with the | |
| goal of generating higher frequency and wider bandwidth THz signals. These | |
| advances hold significant potential for applications in various fields such as | |
| high-resolution imaging, spectroscopy, communications, medical diagnostics, and | |
| more.",2307.02232v1 | |
| 2023-09-06,Mid-infrared optical properties of non-magnetic-metal/CoFeB/MgO heterostructures,"We report on the optical characterization of non-magnetic metal/ferromagnetic | |
| (Co$_{20}$Fe$_{60}$B$_{20}$)/MgO heterostructures and interfaces by using mid | |
| infrared spectroscopic ellipsometry at room temperature. We extracted for the | |
| mid-infrared range the dielectric function of Co$_{20}$Fe$_{60}$B$_{20}$, that | |
| is lacking in literature, from a multisample analysis. From the optical | |
| modelling of the heterostructures we detected and determined the dielectric | |
| tensor properties of a two-dimensional gas (2DEG) forming at the non-magnetic | |
| metal and the CoFeB interface. These properties comprise independent Drude | |
| parameters for the in-plane and out-of plane tensor components, with the latter | |
| having an epsilon-near-zero frequency within our working spectral range. A | |
| feature assigned to spin-orbit coupling (SOC) is identified. Furthermore, it is | |
| found that both, the interfacial properties, 2DEG Drude parameters and SOC | |
| strength, and the apparent dielectric function of the MgO layer depend on the | |
| type of the underlying nonmagnetic metal, namely, Pt, W, or Cu. The results | |
| reported here should be useful in tailoring novel phenomena in such types of | |
| heterostructures by assessing their optical response noninvasively, | |
| complementing existing characterization tools such as angle-resolved | |
| photoemission spectroscopy, and those related to electron/spin transport.",2309.02981v1 | |
| 2023-12-10,"Magnetoelectric Coupling in Pb(Zr,Ti)O3/CoFeB Nanoscale Waveguides Studied by Propagating Spin-Wave Spectroscopy","This study introduces a method for the characterization of the | |
| magnetoelectric coupling in nanoscale Pb(Zr,Ti)O3/CoFeB thin film composites | |
| based on propagating spin-wave spectroscopy. Finite element simulations of the | |
| strain distribution in the devices indicated that the magnetoelastic effective | |
| field in the CoFeB waveguides was maximized in the Damon - Eshbach | |
| configuration. All-electrical broadband propagating spin-wave transmission | |
| measurements were conducted on Pb(Zr,Ti)O3/CoFeB magnetoelectric waveguides | |
| with lateral dimensions down to 700 nm. The results demonstrated that the | |
| spin-wave resonance frequency can be modulated by applying a bias voltage to | |
| Pb(Zr,Ti)O3. The modulation is hysteretic due to the ferroelastic behavior of | |
| Pb(Zr,Ti)O3. An analytical model was then used to correlate the change in | |
| resonance frequency to the induced magnetoelastic field in the magnetostrictive | |
| CoFeB waveguide. We observe a hysteresis magnetoelastic field strength with | |
| values as large as 5.61 mT, and a non-linear magnetoelectric coupling | |
| coefficient with a maximum value of 1.69 mT/V.",2312.05819v1 | |
| 2018-01-12,Anomalous Nernst effect on the nanometer scale: Exploring three-dimensional temperature gradients in magnetic tunnel junctions,"Localized laser heating creates temperature gradients in all directions and | |
| thus leads to three-dimensional electron flux in metallic materials. | |
| Temperature gradients in combination with material magnetization generate | |
| thermomagnetic voltages. The interplay between these direction-dependent | |
| temperature gradients and the magnetization along with their control enable to | |
| manipulate the generated voltages, e.g. in magnetic nanodevices. We identify | |
| the anomalous Nernst effect (ANE) generated on a nanometer length scale by | |
| micrometer sized temperature gradients in magnetic tunnel junctions (MTJs). In | |
| a systematic study, we extract the ANE by analyzing the influence of in-plane | |
| temperature gradients on the tunnel magneto-Seebeck effect (TMS) in three | |
| dimensional devices. To investigate these effects, we utilize in-plane | |
| magnetized MTJs based on CoFeB electrodes with an MgO tunnel barrier. Due to | |
| our measurement configuration, there is no necessity to disentangle the ANE | |
| from the spin Seebeck effect in inverse spin-Hall measurements. The temperature | |
| gradients are created by a tightly focused laser spot. The spatial extent of | |
| the measured effects is defined by the MTJ size, while the spatial resolution | |
| is given by the laser spot size and the step size of its lateral translation. | |
| This method is highly sensitive to low voltages and yields an ANE coefficient | |
| of $K_N\approx 1.6\cdot 10^{-8}\,\mathrm{V/TK}$ for CoFeB. In general, TMS | |
| investigations in MTJs are motivated by the usage of otherwise wasted heat in | |
| magnetic memory devices for read/write operations. Here, the additionally | |
| generated ANE effect allows to expand the MTJs' functionality from simple | |
| memory storage to nonvolatile logic devices and opens new application fields | |
| such as direction dependent temperature sensing with the potential for further | |
| downscaling.",1801.04186v1 | |
| 2021-03-14,Perpendicular magnetic anisotropy in ultra-thin Cu$_2$Sb-type (Mn-Cr)AlGe films onto thermally oxidized silicon substrates,"Perpendicularly magnetized films showing small saturation magnetization, | |
| $M_\mathrm{s}$, are essential for spin-transfer-torque writing type | |
| magnetoresistive random access memories, STT-MRAMs. An intermetallic compound, | |
| {(Mn-Cr)AlGe} of the Cu$_2$Sb-type crystal structure was investigated, in this | |
| study, as a material showing the low $M_\mathrm{s}$ ($\sim 300$ kA/m) and | |
| high-perpendicular magnetic anisotropy, $K_\mathrm{u}$. The layer thickness | |
| dependence of $K_\mathrm{u}$ and effects of Mg-insertion layers at top and | |
| bottom (Mn-Cr)AlGe$|$MgO interfaces were studied in film samples fabricated | |
| onto thermally oxidized silicon substrates to realize high-$K_\mathrm{u}$ in | |
| the thickness range of a few nanometer. Optimum Mg-insertion thicknesses were | |
| 1.4 and 3.0 nm for the bottom and the top interfaces, respectively, which were | |
| relatively thick compared to results in similar insertion effect investigations | |
| on magnetic tunnel junctions reported in previous studies. The cross-sectional | |
| transmission electron microscope images revealed that the Mg-insertion layers | |
| acted as barriers to interdiffusion of Al-atoms as well as oxidization from the | |
| MgO layers. The values of $K_\mathrm{u}$ were about $7 \times 10^5$ and $2 | |
| \times 10^5$ J/m$^3$ at room temperature for 5 and 3 nm-thick (Mn-Cr)AlGe | |
| films, respectively, with the optimum Mg-insertion thicknesses. The | |
| $K_\mathrm{u}$ at a few nanometer thicknesses is comparable or higher than | |
| those reported in perpendicularly magnetized CoFeB films which are | |
| conventionally used in MRAMs, while the $M_\mathrm{s}$ value is one third or | |
| less smaller than those of the CoFeB films. The developed (Mn-Cr)AlGe films are | |
| promising from the viewpoint of not only the magnetic properties, but also the | |
| compatibility to the silicon process in the film fabrication.",2103.07847v2 | |
| 2019-12-08,Multifilamentary character of anticorrelated capacitive and resistive switching in memristive structures based on (CoFeB)x(LiNbO3)100-x nanocomposite,"Resistive and capacitive switching in capacitor metal/nanocomposite/metal | |
| (M/NC/M) structures based on (CoFeB)x(LiNbO3)100-x NC fabricated by ion-beam | |
| sputtering with metal content x $\approx$ 8-20 at. % is studied. The | |
| peculiarity of the structure synthesis was the use of increased oxygen content | |
| ($\approx$ 2*10^-5 Torr) at the initial stage of the NC growth. The NC films, | |
| along with metal nanogranules of 3-6 nm in size, contained a large number of | |
| dispersed Co (Fe) atoms (up to ~10^22 cm^-3). Measurements were performed both | |
| in DC and AC (frequency range 5-13 MHz) regimes. When switching structures from | |
| high-resistance (Roff) to low-resistance (Ron) state, the effect of a strong | |
| increase in their capacity was found, which reaches 8 times at x $\approx$ 15 | |
| at. % and the resistance ratio Roff/Ron $\approx$ 40. The effect is explained | |
| by the synergetic combination of the multifilamentary character of resistive | |
| switching (RS) and structural features of the samples associated, in | |
| particular, with the formation of high-resistance and strongly polarizable | |
| LiNbO3 layer near the bottom electrode of the structures. The proposed model is | |
| confirmed by investigations of RS of two-layer nanoscale M/NC/LiNbO3/M | |
| structures as well as by studies of the magnetization of M/NC/M structures in | |
| the pristine state and after RS.",1912.03726v3 | |
| 2023-05-13,Temperature dependence of magnetic anisotropy and domain wall tuning in BaTiO3(111)/CoFeB multiferroics,"Artificial multiferroics consist of two types of ferroic materials, typically | |
| a ferroelectric and ferromagnet, often coupled interfacially by | |
| magnetostriction induced by the lattice elongations in the ferroelectric. In | |
| BaTiO3 the magnitude of strain induced by these elongations is heavily | |
| temperature dependent, varying greatly between each of the polar crystal phases | |
| and exerting a huge influence over the properties of a coupled magnetic film. | |
| Here we demonstrate that temperature, and thus strain, is an effective means of | |
| controlling the magnetic anisotropy in BaTiO3(111)/CoFeB heterostructures. We | |
| investigate the three polar phases of BaTiO3: tetragonal (T) at room | |
| temperature, orthorhombic (O) below 280 K and rhombohedral (R) below 190 K, | |
| across a total range of 77 K to 420 K. We find two distinct responses; a | |
| step-like change in the anisotropy across the low-temperature phase | |
| transitions, and a sharp high-temperature reduction around the ferroelectric | |
| Curie temperature, measured from hard axis hysteresis loops. Using our | |
| measurements of this anisotropy strength we are then able to show by | |
| micromagnetic simulation the behaviour of all possible magnetic domain wall | |
| states and determine their scaling as a function of temperature. The most | |
| significant changes occur in the head-to-head domain wall states, with a | |
| maximum change of 210 nm predicted across the entire range effectively doubling | |
| the size of the domain wall as compared to room temperature. Notably, similar | |
| changes are seen for both high and low temperatures which suggest different | |
| routes for potential control of magnetic anisotropy and elastically pinned | |
| magnetic domain walls.",2305.07879v1 | |
| 2006-07-21,Tunnel magnetoresistance and robust room temperature exchange bias with multiferroic BiFeO3 epitaxial thin films,"We report on the functionalization of multiferroic BiFeO3 epitaxial films for | |
| spintronics. A first example is provided by the use of ultrathin layers of | |
| BiFeO3 as tunnel barriers in magnetic tunnel junctions with La2/3Sr1/3MnO3 and | |
| Co electrodes. In such structures, a positive tunnel magnetoresistance up to | |
| 30% is obtained at low temperature. A second example is the exploitation of the | |
| antiferromagnetic spin structure of a BiFeO3 film to induce a sizeable (~60 Oe) | |
| exchange bias on a ferromagnetic film of CoFeB, at room temperature. | |
| Remarkably, the exchange bias effect is robust upon magnetic field cycling, | |
| with no indications of training.",0607563v2 | |
| 2006-08-25,Dependence of tunnel magnetoresistance on ferromagnetic electrode materials in MgO-barrier magnetic tunnel junctions,"We investigated the relationship between the tunnel magnetoresistance (TMR) | |
| ratio and the electrode structure in MgO-barrier magnetic tunnel junctions | |
| (MTJs). The TMR ratio in a MTJ with Co40Fe40B20 reference and free layers | |
| reached 355% at the post-deposition annealing temperature of Ta=400 degree C. | |
| When Co50Fe50 or Co90Fe10 is used for the reference layer material, no high TMR | |
| ratio was observed. The key to have high TMR ratio is to have highly oriented | |
| (001) MgO barrier/CoFeB crystalline electrodes. The highest TMR ratio obtained | |
| so far is 450% at Ta = 450 degree C in a pseudo spin-valve MTJ.",0608551v1 | |
| 2007-03-22,Spin-Torque Ferromagnetic Resonance Measurements of Damping in Nanomagnets,"We measure the magnetic damping parameter a in thin film CoFeB and permalloy | |
| (Py) nanomagnets at room temperature using ferromagnetic resonance driven by | |
| microwave frequency spin-transfer torque. We obtain $\alpha_{CoFeB} = 0.014 \pm | |
| 0.003$ and $\alpha_{Py}=0.010 \pm 0.002$, values comparable to measurements for | |
| extended thin films, but significantly less than the effective damping | |
| determined previously for similar nanomagnets by fits to time-domain studies of | |
| large-angle magnetic excitations and magnetic reversal. The greater damping | |
| found for the large amplitude nanomagnet dynamics is attributed to the | |
| nonlinear excitation of non-uniform magnetic modes.",0703577v1 | |
| 2007-08-27,Determination of Penetration Depth of Transverse Spin Current in Ferromagnetic Metals by Spin Pumping,"Spin pumping in nonmagnetic/ferromagnetic metal multilayers is studied both | |
| theoretically and experimentally. We show that the line widths of the | |
| ferromagnetic resonance (FMR) spectrum depend on the thickness of the | |
| ferromagnetic metal layers, which must not be in resonance with the oscillating | |
| magnetic field. We also show that the penetration depths of the transverse spin | |
| current in ferromagnetic metals can be determined by analyzing the line widths | |
| of their FMR spectra. The obtained penetration depths in NiFe, CoFe and CoFeB | |
| were 3.7 [nm], 2.5 [nm] and 12.0 [nm], respectively.",0708.3528v3 | |
| 2007-10-10,Mechanisms of exchange bias with multiferroic BiFeO3 epitaxial thin films,"We have combined neutron scattering and piezoresponse force microscopy to | |
| study the relation between the exchange bias observed in CoFeB/BiFeO3 | |
| heterostructures and the multiferroic domain structure of the BiFeO3 films. We | |
| show that the exchange field scales with the inverse of the ferroelectric and | |
| antiferromagnetic domain size, as expected from Malozemoff's model of exchange | |
| bias extended to multiferroics. Accordingly, polarized neutron reflectometry | |
| reveals the presence of uncompensated spins in the BiFeO3 film at the interface | |
| with the CoFeB. In view of these results we discuss possible strategies to | |
| switch the magnetization of a ferromagnet by an electric field using BiFeO3.",0710.2025v1 | |
| 2009-10-22,MgO barrier-perpendicular magnetic tunnel junctions with CoFe/Pd multilayers and ferromagnetic insertion layers,"The authors studied an effect of ferromagnetic (Co20Fe60B20 or Fe) layer | |
| insertion on tunnel magnetoresistance (TMR) properties of MgO-barrier magnetic | |
| tunnel junctions (MTJs) with CoFe/Pd multilayer electrodes. TMR ratio in MTJs | |
| with CoFeB/MgO/Fe stack reached 67% at an-nealing temperature (Ta) of 200 | |
| degree C and then decreased rapidly at Ta over 250 degree C. The degradation of | |
| the TMR ratio may be related to crystallization of CoFe(B) into fcc(111) or | |
| bcc(011) texture result-ing from diffusion of B into Pd layers. MTJs which were | |
| in-situ annealed at 350oC just after depo-siting bottom CoFe/Pd multilayer | |
| showed TMR ratio of 78% by post annealing at Ta =200 degree C.",0910.4204v1 | |
| 2010-08-09,Detection of bottom ferromagnetic electrode oxidation in magnetic tunnel junctions by magnetometry measurements,"Surface oxidation of the bottom ferromagnetic (FM) electrode, one of the | |
| major detrimental factors to the performance of a Magnetic Tunnel Junction | |
| (MTJ), is difficult to avoid during the fabrication process of the MTJ's tunnel | |
| barrier. Since Co rich alloys are commonly used for the FM electrodes in MTJs, | |
| over-oxidation of the tunnel barrier results in the formation of a CoO | |
| antiferromagnetic (AF) interface layer which couples with the bottom FM | |
| electrode to form a typical AF/FM exchange bias (EB) system. In this work, | |
| surface oxidation of the CoFe and CoFeB bottom electrodes was detected via | |
| magnetometry measurements of exchange-bias characterizations including the EB | |
| field, training effect, uncompensated spin density, and coercivity. Variations | |
| of these parameters were found to be related to the surface oxidation of the | |
| bottom electrode, among them the change of coercivity is most sensitive. | |
| Annealed samples show evidence for an oxygen migration back to the MgO tunnel | |
| barrier by annealing.",1008.1493v1 | |
| 2011-03-16,Spin-Torque Diode Measurements of MgO-Based Magnetic Tunnel Junctions with Asymmetric Electrodes,"We present a detailed study of the spin-torque diode effect in | |
| CoFeB/MgO/CoFe/NiFe magnetic tunnel junctions. From the evolution of the | |
| resonance frequency with magnetic field at different angles, we clearly | |
| identify the free-layer mode and find an excellent agreement with simulations | |
| by taking into account several terms for magnetic anisotropy. Moreover, we | |
| demonstrate the large contribution of the out-of-plane torque in our junctions | |
| with asymmetric electrodes compared to the in-plane torque. Consequently, we | |
| provide a way to enhance the sensitivity of these devices for the detection of | |
| microwave frequency.",1103.3207v1 | |
| 2013-04-09,Paramagnetic Fe_xTa_{1-x} alloys for engineering of perpendicularly magnetized tunnel junctions,"Exchange coupling between two magnetic layers through an interlayer is of | |
| broad interest for numerous recent applications of nano-magnetic systems. In | |
| this Letter we study ferromagnetic exchange coupling through amorphous | |
| paramagnetic Fe-Ta alloys. We show that the exchange coupling depends | |
| exponentially on spacer thickness and scales with the Fe-Ta susceptibility, | |
| which can be tuned via the alloy composition and/or temperature. Such materials | |
| are of high interest for the engineering of perpendicularly magnetized | |
| CoFeB-MgO based tunnel junctions as it enables ferromagnetic coupling of | |
| magnetic layers with differing crystalline lattices, suppresses dead layers and | |
| can act as an inter-diffusion barrier during annealing.",1304.2763v1 | |
| 2013-08-29,Control of Propagating Spin Waves via Spin Transfer Torque in a Metallic Bilayer Waveguide,"We investigate the effect of a direct current on propagating spin waves in a | |
| CoFeB/Ta bilayer structure. Using the micro-Brillouin light scattering | |
| technique, we observe that the spin wave amplitude may be attenuated or | |
| amplified depending on the direction of the current and the applied magnetic | |
| field. Our work suggests an effective approach for electrically controlling the | |
| propagation of spin waves in a magnetic waveguide and may be useful in a number | |
| of applications such as phase locked nano-oscillators and hybrid information | |
| processing devices.",1308.6357v2 | |
| 2014-01-29,Nonreciprocal Dispersion of Spin Waves in Ferromagnetic Thin Films Covered with a Finite-Conductivity Metal,"We study the effect of one-side metallization of a uniform ferromagnetic thin | |
| film on its spin-wave dispersion relation in the Damon-Eshbach geometry. Due to | |
| the finite conductivity of the metallic cover layer on the ferromagnetic film | |
| the spin-wave dispersion relation may be nonreciprocal only in a limited | |
| wave-vector range. We provide an approximate analytical solution for the | |
| spin-wave frequency, discuss its validity and compare it with numerical | |
| results. The dispersion is analyzed systematically by varying the parameters of | |
| the ferromagnetic film, the metal cover layer and the value of the external | |
| magnetic field. The conclusions drawn from this analysis allow us to define a | |
| structure based on a 30 nm thick CoFeB film with an experimentally accessible | |
| nonreciprocal dispersion relation in a relatively wide wave-vector range.",1401.7454v1 | |
| 2014-02-18,Switching Properties in Magnetic Tunnel Junctions with Interfacial Perpendicular Anisotropy: Micromagnetic Study,"The role of universal memory can be successfully satisfied by magnetic tunnel | |
| junctions (MTJs) where the writing mechanism is based on spin-transfer torque | |
| (STT). An improvement in the switching properties (lower switching current | |
| density maintaining the thermal stability) has been achieved in MTJs with | |
| interfacial perpendicular anisotropy (IPA) at the interface between CoFeB and | |
| MgO. In this paper, micromagnetic simulations point out the influence of IPA | |
| and saturation magnetization (MS) on the properties of fast magnetization | |
| reversal achieved in 5, 10 and 20 ns. Both cases of in-plane and out-of-plane | |
| free layer are considered. In addition, the thermal effect is included for the | |
| in-plane switching at 20 ns and a complete analysis of energy dissipation | |
| during the switching is illustrated. This study can provide useful information | |
| for the design of STT-based memories.",1402.4352v1 | |
| 2014-07-23,Deterministic Domain Wall Motion Orthogonal To Current Flow Due To Spin Orbit Torque,"Deterministic control of domain walls orthogonal to the direction of current | |
| flow is demonstrated by exploiting spin orbit torque in a perpendicularly | |
| polarized Ta/CoFeB/MgO multilayer in presence of an in-plane magnetic field. | |
| Notably, such orthogonal motion with respect to current flow is not possible | |
| from traditional spin transfer torque driven domain wall propagation even in | |
| presence of an external magnetic field. Reversing the polarity of either the | |
| current flow or the in-plane field is found to reverse the direction of the | |
| domain wall motion. From these measurements, which are unaffected by any | |
| conventional spin transfer torque by symmetry, we estimate the spin orbit | |
| torque efficiency of Ta to be 0.08.",1407.6137v1 | |
| 2014-11-19,Universal domain wall dynamics under electric field in Ta/CoFeB/MgO devices with perpendicular anisotropy,"Electric field effects in ferromagnetic/oxide dielectric structures provide a | |
| new route to control domain wall (DW) dynamics with low power dissipation. | |
| However, electric field effects on DW velocities have only been observed so far | |
| in the creep regime where DW velocities are low due to strong interactions with | |
| pinning sites. Here, we show gate voltage modulation of DW velocities ranging | |
| from the creep to the flow regime in Ta/Co40Fe40B20/MgO/TiO2 structures with | |
| perpendicular magnetic anisotropy. We demonstrate a universal description of | |
| the role of applied electric fields in the various pinning dependent regimes by | |
| taking into account an effective magnetic field being linear with the electric | |
| field. In addition, the electric field effect is found to change sign in the | |
| Walker regime. Our work opens new opportunities for the study and optimization | |
| of electric field effect at ferromagnetic metal/insulator interfaces.",1411.5267v2 | |
| 2015-03-02,Measuring the magnetic moment density in patterned ultrathin ferromagnets with submicron resolution,"We present a new approach to infer the surface density of magnetic moments | |
| $I_s$ in ultrathin ferromagnetic films with perpendicular anisotropy. It relies | |
| on quantitative stray field measurements with an atomic-size magnetometer based | |
| on the nitrogen-vacancy center in diamond. The method is applied to | |
| microstructures patterned in a 1-nm-thick film of CoFeB. We report measurements | |
| of $I_s$ with a few percent uncertainty and a spatial resolution in the range | |
| of $(100$ nm)$^2$, an improvement by several orders of magnitude over existing | |
| methods. As an example of application, we measure the modifications of $I_s$ | |
| induced by local irradiation with He$^+$ ions in an ultrathin ferromagnetic | |
| wire. This method offers a new route to study variations of magnetic properties | |
| at the nanoscale.",1503.00705v1 | |
| 2015-03-25,Spin Hall torque driven chiral domain walls in magnetic heterostructures,"The motion of magnetic domain walls in ultrathin magnetic heterostructures | |
| driven by current via the spin Hall torque is described. We show results from | |
| perpendicularly magnetized CoFeB|MgO heterostructures with various heavy metal | |
| underlayers. The domain wall moves along or against the current flow depending | |
| on the underlayer material. The direction to which the domain wall moves is | |
| associated with the chirality of the domain wall spiral formed in these | |
| heterostructures. The one-dimensional model is used to describe the | |
| experimental results and extract parameters such as the Dzyaloshinskii-Moriya | |
| exchange constant which is responsible for the formation of the domain wall | |
| spiral. Fascinating effects arising from the control of interfaces in magnetic | |
| heterostructures are described.",1503.07250v1 | |
| 2015-03-31,Spin Hall magnetoresistance in metallic bilayers,"Spin Hall magnetoresistance (SMR) is studied in metallic bilayers that | |
| consist of heavy metal (HM) layer and a ferromagnetic metal (FM) layer. We find | |
| nearly a ten-fold increase of SMR in W/CoFeB compared to previously studied | |
| HM/ferromagnetic insulator (FI) systems. The SMR increases with decreasing | |
| temperature despite the negligible change in the W layer resistivity with | |
| temperature. A model is developed to account for the absorption of the | |
| longitudinal spin current to the FM layer, one of the key characteristics of a | |
| metallic ferromagnet. We find that the model not only quantitatively describes | |
| the HM layer thickness dependence of SMR, allowing accurate estimation of the | |
| spin Hall angle and the spin diffusion length of the HM layer, but also can | |
| account for the temperature dependence of SMR by assuming a temperature | |
| dependent spin polarization of the FM layer. These results illustrate the | |
| unique role a metallic ferromagnetic layer plays in defining spin transmission | |
| across the HM/FM interface.",1503.08903v2 | |
| 2015-08-18,Quasistatic and Pulsed Current-Induced Switching with Spin-Orbit Torques in Ultrathin Films with Perpendicular Magnetic Anisotropy,"Spin-orbit interaction derived spin torques provide a means of reversing the | |
| magnetization of perpendicularly magnetized ultrathin films with currents that | |
| flow in the plane of the layers. A basic and critical question for applications | |
| is the speed and efficiency of switching with nanosecond current pulses. Here | |
| we investigate and contrast the quasistatic (slowly swept current) and pulsed | |
| current-induced switching characteristics of micron scale Hall crosses | |
| consisting of very thin ($<1$ nm) perpendicularly magnetized CoFeB layers on | |
| $\beta$-Ta. While complete magnetization reversal is found at a threshold | |
| current density in the quasistatic case, short duration ($\leq 10$ ns) larger | |
| amplitude pulses ($\simeq 10 \times$ the quasistatic threshold current) lead to | |
| only partial magnetization reversal and domain formation. We associate the | |
| partial reversal with the limited time for reversed domain expansion during the | |
| pulse.",1508.04336v1 | |
| 2015-08-24,Origin of robust interaction of spin waves with a single skyrmion in perpendicularly magnetized nanostripes,"We studied interactions between propagating spin waves (SWs) and a single | |
| skyrmion in a perpendicularly magnetized CoFeB nanostripe where the magnetic | |
| layer is interfaced with W and MgO. Micromagnetic numerical calculations | |
| revealed that robust interactions between the incident SWs and the skyrmion | |
| give rise to considerable forward skyrmion motions for specific SW frequencies | |
| (e.g., here: fsw = 12 - 19 GHz). Additionally, it was found that there exists a | |
| sufficiently low threshold field amplitude, e.g., 0.1 kOe for the fsw = 15 GHz | |
| SWs. This frequency-dependent interaction originated from the robust coupling | |
| of the SWs with the internal modes of the skyrmion, through the SWs' linear | |
| momentum transfer torque acting on the skyrmion. This work provides for | |
| all-magnetic control of skyrmion motions without electronic currents, and | |
| facilitates further understanding of the interactions between magnons and | |
| topological solitons in constricted geometries.",1508.05682v1 | |
| 2015-12-11,Correlation between the spin Hall angle and the structural phases of early 5d transition metals,"We have studied the relationship between the structure and the spin Hall | |
| angle of the early 5d transition metals in X/CoFeB/MgO (X=Hf, Ta, W, Re) | |
| heterostructures. Spin Hall magnetoresistance (SMR) is used to characterize the | |
| spin Hall angle of the heavy metals. Transmission electron microscopy images | |
| show that all underlayers are amorphous-like when their thicknesses are small, | |
| however, crystalline phases emerge as the thickness is increased for certain | |
| elements. We find that the heavy metal layer thickness dependence of the SMR | |
| reflects these changes in structure. The spin Hall angle largest | |
| |\theta$_{SH}$| of Hf, Ta, W and Re (~0.11, 0.10, 0.23 and 0.07, respectively) | |
| is found when the dominant phase is amorphous-like. We find that the | |
| amorphous-like phase not only possesses large resistivity but also exhibits | |
| sizeable spin Hall conductivity, which both contribute to the emergence of the | |
| large spin Hall angle.",1512.03529v1 | |
| 2016-02-24,Exchange stiffness in ultrathin perpendicularly-magnetized CoFeB layers determined using spin wave spectroscopy,"We measure the frequencies of spin waves in nm-thick perpendicularly | |
| magnetized FeCoB systems, and model the frequencies to deduce the exchange | |
| stiffness of this material in the ultrathin limit. For this, we embody the | |
| layers in magnetic tunnel junctions patterned into circular nanopillars of | |
| diameters ranging from 100 to 300 nm and we use magneto-resistance to determine | |
| which rf-current frequencies are efficient in populating the spin wave modes. | |
| Micromagnetic calculations indicate that the ultrathin nature of the layer and | |
| the large wave vectors used ensure that the spin wave frequencies are | |
| predominantly determined by the exchange stiffness, such that the number of | |
| modes in a given frequency window can be used to estimate the exchange. For 1 | |
| nm layers the experimental data are consistent with an exchange stiffness A= 20 | |
| pJ/m, which is slightly lower that its bulk counterpart. The thickness | |
| dependence of the exchange stiffness has strong implications for the numerous | |
| situations that involve ultrathin films hosting strong magnetization gradients, | |
| and the micromagnetic description thereof.",1602.07421v1 | |
| 2016-04-15,Twist in the bias-dependence of spin-torques in magnetic tunnel junctions,"The spin-torque in magnetic tunnel junctions possesses two components that | |
| both depend on the applied voltage. Here, we develop a new method for the | |
| accurate extraction of this bias-dependence from experiments over large voltage | |
| ranges. We study several junctions with different magnetic layer structures of | |
| the top electrode. Our results obtained on junctions with symmetric CoFeB | |
| electrodes agree well with theoretical calculations. The bias-dependences of | |
| asymmetric samples, with top electrodes containing NiFe, however, are twisted | |
| compared to the quadratic form generally assumed. Our measurements reveal the | |
| complexity of spin-torque mechanisms at large bias.",1604.04517v1 | |
| 2016-04-16,A broadband Ferromagnetic Resonance dipper probe for magnetic damping measurements from 4.2 K to 300 K,"A dipper probe for broadband Ferromagnetic Resonance (FMR) operating from 4.2 | |
| K to room temperature is described. The apparatus is based on a 2-port | |
| transmitted microwave signal measurement with a grounded coplanar waveguide. | |
| The waveguide generates a microwave field and records the sample response. A | |
| 3-stage dipper design is adopted for fast and stable temperature control. The | |
| temperature variation due to FMR is in the milli-Kelvin range at liquid helium | |
| temperature. We also designed a novel FMR probe head with a spring-loaded | |
| sample holder. Improved signal-to-noise ratio and stability compared to a | |
| common FMR head are achieved. Using a superconducting vector magnet we | |
| demonstrate Gilbert damping measurements on two thin film samples using a | |
| vector network analyzer with frequency up to 26 GHz: 1) A Permalloy film of 5 | |
| nm thickness and 2) a CoFeB film of 1.5 nm thickness. Experiments were | |
| performed with the applied magnetic field parallel and perpendicular to the | |
| film plane.",1604.04688v1 | |
| 2016-05-18,Electrical control over perpendicular magnetization switching driven by spin-orbit torques,"Flexible control of magnetization switching by electrical manners is crucial | |
| for applications of spin-orbitronics. Besides of a switching current that is | |
| parallel to an applied field, a bias current that is normal to the switching | |
| current is introduced to tune the magnitude of effective damping-like and | |
| field-like torques and further to electrically control magnetization switching. | |
| Symmetrical and asymmetrical control over the critical switching current by the | |
| bias current with opposite polarities is both realized in Pt/Co/MgO and | |
| $\alpha$-Ta/CoFeB/MgO systems, respectively. This research not only identifies | |
| the influences of field-like and damping-like torques on switching process but | |
| also demonstrates an electrical method to control it.",1605.05569v1 | |
| 2016-09-14,Rashba-Edelstein Magnetoresistance in Metallic Heterostructure,"We report the observation of magnetoresistance originating from Rashba | |
| spin-orbit coupling (SOC) in a metallic heterostructure: the Rashba-Edelstein | |
| (RE) magnetoresistance. We show that the simultaneous action of the direct and | |
| inverse RE effects in a Bi/Ag/CoFeB trilayer couples current-induced spin | |
| accumulation to the electric resistance. The electric resistance changes with | |
| the magnetic-field angle, reminiscent of the spin Hall magnetoresistance, | |
| despite the fact that bulk SOC is not responsible for the magnetoresistance. We | |
| further found that, even when the magnetization is saturated, the resistance | |
| increases with increasing the magnetic-field strength, which is attributed to | |
| the Hanle magnetoresistance in this system.",1609.04122v1 | |
| 2016-11-03,Scalable synchronization of spin-Hall oscillators in out-of-plane field,"A strategy for a scalable synchronization of an array of spin-Hall | |
| oscillators (SHOs) is illustrated. In detail, we present micromagnetic | |
| simulations of two and five SHOs realized by means of couples of triangular | |
| golden contacts on the top of a Pt/CoFeB/Ta trilayer. Results highlight that | |
| the synchronization occurs for the whole current region that gives rise to the | |
| excitation of self-oscillations. This is linked to the role of the | |
| magnetodipolar coupling, which is the phenomenon driving the synchronization | |
| when the distance between oscillators is not too large. Synchronization turns | |
| out to be also robust against geometrical differences of the contacts, | |
| simulated by considering variable distances between the tips ranging from 100nm | |
| to 200nm. Besides, it entails an enlargement of the radiation pattern that can | |
| be useful for the generation of spin-waves in magnonics applications. | |
| Simulations performed to study the effect of the interfacial | |
| Dzyaloshinskii-Moriya interaction show nonreciprocity in spatial propagation of | |
| the synchronized spin-wave. The simplicity of the geometry and the robustness | |
| of the achieved synchronization make this design of array of SHOs scalable for | |
| a larger number of synchronized oscillators.",1611.01227v1 | |
| 2017-01-23,Understanding stability diagram of perpendicular magnetic tunnel junctions,"Perpendicular magnetic tunnel junctions (MTJ) with a bottom pinned reference | |
| layer and a composite free layer (FL) are investigated. Different thicknesses | |
| of the FL were tested to obtain an optimal balance between tunneling | |
| magnetoresistance (TMR) ratio and perpendicular magnetic anisotropy. After | |
| annealing at 400 $^\circ$C, the TMR ratio for 1.5 nm thick CoFeB sublayer | |
| reached 180 % at room temperature and 280 % at 20 K with an MgO tunnel barrier | |
| thickness corresponding to the resistance area product RA = 10 | |
| Ohm$\mathrm{\mu}$m$^2$. The voltage vs. magnetic field stability diagrams | |
| measured in pillar-shaped MTJs with 130 nm diameter indicate the competition | |
| between spin transfer torque (STT), voltage controlled magnetic anisotropy | |
| (VCMA) and temperature effects in the switching process. An extended stability | |
| phase diagram model that takes into account all three parameters and the | |
| effective damping measured independently using broadband ferromagnetic | |
| resonance technique enabled the determination of both STT and VCMA coefficients | |
| that are responsible for the FL magnetization switching.",1701.06411v1 | |
| 2017-03-29,Ultrabroadband single-cycle terahertz pulses with peak fields of 300 kV cm$^{-1}$ from a metallic spintronic emitter,"To explore the capabilities of metallic spintronic thin-film stacks as a | |
| source of intense and broadband terahertz electromagnetic fields, we excite a | |
| W/CoFeB/Pt trilayer on a large-area glass substrate (diameter of 7.5 cm) by a | |
| femtosecond laser pulse (energy 5.5 mJ, duration 40 fs, wavelength 800 nm). | |
| After focusing, the emitted terahertz pulse is measured to have a duration of | |
| 230 fs, a peak field of 300 kV cm$^{-1}$ and an energy of 5 nJ. In particular, | |
| the waveform exhibits a gapless spectrum extending from 1 to 10 THz at 10% of | |
| amplitude maximum, thereby facilitating nonlinear control over matter in this | |
| difficult-to-reach frequency range and on the sub-picosecond time scale.",1703.09970v1 | |
| 2017-07-15,Stochastic Spin-Orbit Torque Devices as Elements for Bayesian Inference,"Probabilistic inference from real-time input data is becoming increasingly | |
| popular and may be one of the potential pathways at enabling cognitive | |
| intelligence. As a matter of fact, preliminary research has revealed that | |
| stochastic functionalities also underlie the spiking behavior of neurons in | |
| cortical microcircuits of the human brain. In tune with such observations, | |
| neuromorphic and other unconventional computing platforms have recently started | |
| adopting the usage of computational units that generate outputs | |
| probabilistically, depending on the magnitude of the input stimulus. In this | |
| work, we experimentally demonstrate a spintronic device that offers a direct | |
| mapping to the functionality of such a controllable stochastic switching | |
| element. We show that the probabilistic switching of Ta/CoFeB/MgO | |
| heterostructures in presence of spin-orbit torque and thermal noise can be | |
| harnessed to enable probabilistic inference in a plethora of unconventional | |
| computing scenarios. This work can potentially pave the way for hardware that | |
| directly mimics the computational units of Bayesian inference.",1707.04687v2 | |
| 2017-09-08,Tunneling magnetoresistance of perpendicular CoFeB-based junctions with exchange bias,"Recently, magnetic tunnel junctions with perpendicular magnetized electrodes | |
| combined with exchange bias films have attracted large interest. In this paper | |
| we examine the tunnel magnetoresistance of | |
| Ta/Pd/IrMn/Co-Fe/Ta/Co-Fe-B/MgO/Co-Fe-B/capping/Pd magnetic tunnel junctions in | |
| dependence on the capping layer, i.e., Hf or Ta. In these stacks perpendicular | |
| exchange bias fields of -500\,Oe along with perpendicular magnetic anisotropy | |
| are combined. A tunnel magnetoresistance of $(47.2\pm 1.4)\%$ for the Hf-capped | |
| sample was determined compared to the Ta one $(42.6\pm 0.7)\%$ at room | |
| temperature. Interestingly, this observation is correlated to the higher boron | |
| absorption of Hf compared to Ta which prevents the suppression of | |
| $\Delta_{\textrm{1}}$ channel and leads to higher tunnel magnetoresistance | |
| values. Furthermore, the temperature dependent coercivities of the soft | |
| electrodes of both samples are mainly described by the Stoner-Wohlfarth model | |
| including thermal fluctuations. Slight deviations at low temperatures can be | |
| attributed to a torque on the soft electrode that is generated by the pinned | |
| magnetic layer system.",1709.02607v1 | |
| 2017-09-12,Scaling of Dzyaloshinskii Moriya interaction at heavy metal and ferromagnetic metal interfaces,"The Dzyaloshinskii Moriya Interaction (DMI) at the heavy metal (HM) and | |
| ferromagnetic metal (FM) interface has been recognized as a key ingredient in | |
| spintronic applications. Here we investigate the chemical trend of DMI on the | |
| 5d band filling (5d^3~5d^10) of the HM element in HM/CoFeB/MgO multilayer thin | |
| films. DMI is quantitatively evaluated by measuring asymmetric spin wave | |
| dispersion using Brillouin light scattering. Sign reversal and 20 times | |
| modification of the DMI coefficient D have been measured as the 5d HM element | |
| is varied. The chemical trend can be qualitatively understood by considering | |
| the 5d and 3d bands alignment at the HM/FM interface and the subsequent orbital | |
| hybridization around the Fermi level. Furthermore, a positive correlation is | |
| observed between DMI and spin mixing conductance at the HM/FM interfaces. Our | |
| results provide new insights into the interfacial DMI for designing future | |
| spintronic devices.",1709.03961v1 | |
| 2017-11-09,Room Temperature Giant Charge-to-Spin Conversion at SrTiO3/LaAlO3 Oxide Interface,"Two-dimensional electron gas (2DEG) formed at the interface between SrTiO3 | |
| (STO) and LaAlO3 (LAO) insulating layer is supposed to possess strong Rashba | |
| spin-orbit coupling. To date, the inverse Edelstein effect (i.e. spin-to-charge | |
| conversion) in the 2DEG layer is reported. However, the direct effect of | |
| charge-to-spin conversion, an essential ingredient for spintronic devices in a | |
| current induced spin-orbit torque scheme, has not been demonstrated yet. Here | |
| we show, for the first time, a highly efficient spin generation with the | |
| efficiency of ~6.3 in the STO/LAO/CoFeB structure at room temperature by using | |
| spin torque ferromagnetic resonance. In addition, we suggest that the spin | |
| transmission through the LAO layer at high temperature range is attributed to | |
| the inelastic tunneling via localized states in the LAO band gap. Our findings | |
| may lead to potential applications in the oxide insulator based spintronic | |
| devices.",1711.03268v1 | |
| 2017-12-05,Studies of CoFeB crystalline structure grown on PbSnTe topological insulator substrate,"Co40Fe40B20 layers were grown on the Pb0.71Sn0.29Te topological insulator | |
| substrates by laser molecular beam epitaxy (LMBE) method, and the growth | |
| conditions were studied. The possibility of growing epitaxial layers of a | |
| ferromagnet on the surface of a topological insulator was demonstrated for the | |
| first time. The Co40Fe40B20 layers obtained have a bcc crystal structure with a | |
| crystalline (111) plane parallel to the (111) PbSnTe plane. The use of | |
| three-dimensional mapping in the reciprocal space of reflection high electron | |
| diffraction (RHEED) patterns made it possible to determine the epitaxial | |
| relationship of main crystallographic axes between the film and the substrate | |
| of topological insulator. Quenching of some reflections in diffraction pattern | |
| allows confirmation of the substrate stoichiometry.",1712.01585v3 | |
| 2017-12-23,Shape anisotropy revisited in single-digit nanometer magnetic tunnel junctions,"Nanoscale magnetic tunnel junction plays a pivotal role in magnetoresistive | |
| random access memories. Successful implementation depends on a simultaneous | |
| achievement of low switching current for the magnetization switching by | |
| spin-transfer torque and high thermal stability, along with a continuous | |
| reduction of junction size. Perpendicular-easy-axis CoFeB/MgO stacks possessing | |
| interfacial anisotropy have paved the way down to 20-nm scale, below which a | |
| new approach needs to be explored. Here we show magnetic tunnel junctions that | |
| satisfy the requirements at ultrafine scale by revisiting shape anisotropy, | |
| which is a classical part of magnetic anisotropy but has not been fully | |
| utilized in the current perpendicular systems. Magnetization switching solely | |
| driven by current is achieved for junctions smaller than 10 nm where sufficient | |
| thermal stability is provided by shape anisotropy without adopting new material | |
| systems. This work is expected to push forward the development of magnetic | |
| tunnel junctions towards single-digit-nm-scale nano-magnetics/spintronics.",1712.08774v1 | |
| 2018-01-17,Hartman effect for spin waves in exchange regime,"Hartman effect for spin waves tunnelling through a barrier in a thin magnetic | |
| film is considered theoretically. The barrier is assumed to be created by a | |
| locally increased magnetic anisotropy field. The considerations are focused on | |
| a nanoscale system operating in the exchange-dominated regime. We derive the | |
| formula for group delay $\tau_{gr}$ of spin wave package and show that | |
| $\tau_{gr}$ saturates with increasing barrier width, which is a signature of | |
| the Hartman effect predicted earlier for photonic and electronic systems. In | |
| our calculations we consider the general boundary exchange conditions which | |
| take into account different strength of exchange coupling between the barrier | |
| and its surrounding. As a system suitable for experimental observation of the | |
| Hartman effect we propose a CoFeB layer with perpendicular magnetic anisotropy | |
| induced by a MgO overlayer.",1801.05876v3 | |
| 2018-03-22,Voltage Control of Magnetic Monopoles in Artificial Spin Ice,"Current research on artificial spin ice (ASI) systems has revealed unique | |
| hysteretic memory effects and mobile quasi-particle monopoles controlled by | |
| externally applied magnetic fields. Here, we numerically demonstrate a | |
| strain-mediated multiferroic approach to locally control the ASI monopoles. The | |
| magnetization of individual lattice elements is controlled by applying voltage | |
| pulses to the piezoelectric layer resulting in strain-induced magnetic | |
| precession timed for 180 degree reorientation. The model demonstrates localized | |
| voltage control to move the magnetic monopoles across lattice sites, in CoFeB, | |
| Ni, and FeGa based ASI$'$s. The switching is achieved at frequencies near | |
| ferromagnetic resonance and requires energies below 620 aJ. The results | |
| demonstrate that ASI monopoles can be efficiently and locally controlled with a | |
| strain-mediated multiferroic approach.",1803.08598v1 | |
| 2018-05-09,Programmable control of spin-wave transmission in a domain-wall spin valve,"Active manipulation of spin waves is essential for the development of | |
| magnon-based technologies. Here, we demonstrate programmable spin-wave | |
| filtering by resetting the spin structure of a pinned 90$^\circ$ N\'{e}el | |
| domain wall in a continuous CoFeB film with abrupt rotations of uniaxial | |
| magnetic anisotropy. Using phase-resolved micro-focused Brillouin light | |
| scattering and micromagnetic simulations, we show that broad 90$^\circ$ | |
| head-to-head or tail-to-tail magnetic domain walls are transparent to spin | |
| waves over a broad frequency range. In contrast, magnetic switching to a | |
| 90$^\circ$ head-to-tail configuration produces much narrower domain walls at | |
| the same pinning locations. Spin waves are strongly reflected by a resonance | |
| mode in these magnetic domain walls. Based on these results, we propose a | |
| magnetic spin-wave valve with two parallel domain walls. Switching the | |
| spin-wave valve from an open to a close state changes the transmission of spin | |
| waves from nearly 100% to 0% at the resonance frequency. This active control | |
| over spin-wave transport could be utilized in magnonic logic devices or | |
| non-volatile memory elements.",1805.03470v1 | |
| 2018-05-10,Anomalous spin Hall magnetoresistance in Pt/Co bilayers,"We have studied the spin Hall magnetoresistance (SMR), the magnetoresistance | |
| within the plane transverse to the current flow, of Pt/Co bilayers. We find | |
| that the SMR increases with increasing Co thickness: the effective spin Hall | |
| angle for bilayers with thick Co exceeds the reported values of Pt when a | |
| conventional drift-diffusion model is used. An extended model including spin | |
| transport within the Co layer cannot account for the large SMR. To identify its | |
| origin, contributions from other sources are studied. For most bilayers, the | |
| SMR increases with decreasing temperature and increasing magnetic field, | |
| indicating that magnon-related effects in the Co layer play little role. | |
| Without the Pt layer, we do not observe the large SMR found for the Pt/Co | |
| bilayers with thick Co. Implementing the effect of the so-called interface | |
| magnetoresistance and the textured induced anisotropic scattering cannot | |
| account for the Co thickness dependent SMR. Since the large SMR is present for | |
| W/Co but its magnitude reduces in W/CoFeB, we infer its origin is associated | |
| with a particular property of Co.",1805.03843v1 | |
| 2019-04-25,Low damping magnetic properties and perpendicular magnetic anisotropy with strong volume contribution in the Heusler alloy Fe1.5CoGe,"We present a study of the dynamic magnetic properties of TiN-buffered | |
| epitaxial thin films of the Heusler alloy Fe$_{1.5}$CoGe. Thickness series | |
| annealed at different temperatures are prepared and the magnetic damping is | |
| measured, a lowest value of $\alpha=2.18\times 10^{-3}$ is obtained. The | |
| perpendicular magnetic anisotropy properties in Fe$_{1.5}$CoGe/MgO are also | |
| characterized. The evolution of the interfacial perpendicular anisotropy | |
| constant $K^{\perp}_{\rm S}$ with the annealing temperature is shown and | |
| compared with the widely used CoFeB/MgO interface. A large volume contribution | |
| to the perpendicular anisotropy of $(4.3\pm0.5)\times 10^{5}$ $\rm J/m^3$ is | |
| also found, in contrast with vanishing bulk contribution in common Co- and | |
| Fe-based Heusler alloys.",1904.11247v1 | |
| 2019-10-11,Investigation of spin orbit torque driven dynamics in ferromagnetic heterostructures,"We use time-resolved (TR) measurements based on the polar magneto-optical | |
| Kerr effect (MOKE) to study the magnetization dynamics excited by spin orbit | |
| torques in Py (Permalloy)/Pt and Ta/CoFeB bilayers. The analysis reveals that | |
| the field-like (FL) spin orbit torque (SOT) dominates the amplitude of the | |
| first oscillation cycle of the magnetization precession and the damping-like | |
| (DL) torque determines the final steady-state magnetization. In our bilayer | |
| samples, we have extracted the effective fields, hFL and hDL, of the two SOTs | |
| from the time-resolved magnetization oscillation spectrum. The extracted values | |
| are in good agreement with those extracted from time-integrated DCMOKE | |
| measurements, suggesting that the SOTs do not change at high frequencies. We | |
| also find that the amplitude ratio of the first oscillation to steady state is | |
| linearly proportional to the ratio hFL/hDL. The first oscillation amplitude is | |
| inversely proportional to, whereas the steady state value is independent of, | |
| the applied external field along the current direction.",1910.04945v1 | |
| 2019-10-28,The spin Hall effect of Bi-Sb alloys driven by thermally excited Dirac-like electrons,"We have studied the charge to spin conversion in Bi$_{1-x}$Sb$_x$/CoFeB | |
| heterostructures. The spin Hall conductivity (SHC) of the sputter deposited | |
| heterostructures exhibits a high plateau at Bi-rich compositions, corresponding | |
| to the topological insulator phase, followed by a decrease of SHC for Sb-richer | |
| alloys, in agreement with the calculated intrinsic spin Hall effect of | |
| Bi$_{1-x}$Sb$_x$ alloy. The SHC increases with increasing thickness of the | |
| Bi$_{1-x}$Sb$_x$ alloy before it saturates, indicating that it is the bulk of | |
| the alloy that predominantly contributes to the generation of spin current; the | |
| topological surface states, if present in the films, play little role. | |
| Surprisingly, the SHC is found to increase with increasing temperature, | |
| following the trend of carrier density. These results suggest that the large | |
| SHC at room temperature, with a spin Hall efficiency exceeding 1 and an | |
| extremely large spin current mobility, is due to increased number of | |
| Dirac-like, thermally-excited electrons in the $L$ valley of the narrow gap | |
| Bi$_{1-x}$Sb$_x$ alloy.",1910.12433v1 | |
| 2018-02-07,Breaking the current density threshold in spin-orbit-torque magnetic random access memory,"Spin-orbit-torque magnetic random access memory (SOT-MRAM) is a promising | |
| technology for the next generation of data storage devices. The main bottleneck | |
| of this technology is the high reversal current density threshold. This | |
| outstanding problem of SOT-MRAM is now solved by using a current density of | |
| constant magnitude and varying flow direction that reduces the reversal current | |
| density threshold by a factor of more than the Gilbert damping coefficient. The | |
| Euler-Lagrange equation for the fastest magnetization reversal path and the | |
| optimal current pulse are derived for an arbitrary magnetic cell. The | |
| theoretical limit of minimal reversal current density and current density for a | |
| GHz switching rate of the new reversal strategy for CoFeB/Ta SOT-MRAMs are | |
| respectively of the order of $10^5$ A/cm$^2$ and $10^6$ A/cm$^2$ far below | |
| $10^7$ A/cm$^2$ and $10^8$ A/cm$^2$ in the conventional strategy. Furthermore, | |
| no external magnetic field is needed for a deterministic reversal in the new | |
| strategy.",1802.02415v1 | |
| 2018-12-05,Single spin sensing of domain wall structure and dynamics in a thin film skyrmion host,"Skyrmions are nanoscale magnetic structures with features promising for | |
| future low-power memory or logic devices. In this work, we demonstrate novel | |
| scanning techniques based on nitrogen vacancy center magnetometry that | |
| simultaneously probe both the magnetic dynamics and structure of room | |
| temperature skyrmion bubbles in a thin film system Ta/CoFeB/MgO. We confirm the | |
| handedness of the Dzyaloshinskii-Moriya interaction in this material and | |
| extract the helicity angle of the skyrmion bubbles. Our measurements also show | |
| that the skyrmion bubbles in this material change size in discrete steps, | |
| dependent on the local pinning environment, with their average size determined | |
| dynamically as their domain walls hop between pinning sites. In addition, an | |
| increase in magnetic field noise is observed near all skyrmion bubble domain | |
| walls. These measurements highlight the importance of interactions between | |
| internal degrees of freedom of skyrmion bubble domain walls and pinning sites | |
| in thin film systems. Our observations have relevance for future devices based | |
| on skyrmion bubbles where pinning interactions will determine important aspects | |
| of current-driven motion.",1812.01764v1 | |
| 2019-06-04,High frequency voltage-induced ferromagnetic resonance in magnetic tunnel junctions,"Voltage-induced ferromagnetic resonance (V-FMR) in magnetic tunnel junctions | |
| (MTJs) with a W buffer is investigated. Perpendicular magnetic anisotropy (PMA) | |
| energy is controlled by both thickness of a CoFeB free layer deposited directly | |
| on the W buffer and a post-annealing process at different temperatures. The PMA | |
| energy as well as the magnetization damping are determined by analysing | |
| field-dependent FMR signals in different field geometries. An optimized MTJ | |
| structure enabled excitation of V-FMR at frequencies exceeding 30 GHz. The | |
| macrospin modelling is used to analyse the field- and angular-dependence of the | |
| V-FMR signal and to support experimental magnetization damping extraction.",1906.01301v1 | |
| 2022-02-01,Numerical Model Of Harmonic Hall Voltage Detection For Spintronic Devices,"We present a numerical macrospin model for harmonic voltage detection in | |
| multilayer spintronic devices. The core of the computational backend is based | |
| on the Landau-Lifshitz-Gilbert-Slonczewski equation, which combines high | |
| performance with satisfactory, for large-scale applications, agreement with the | |
| experimental results. We compare the simulations with the experimental findings | |
| in Ta/CoFeB bilayer system for angular- and magnetic field-dependent resistance | |
| measurements, electrically detected magnetisation dynamics, and harmonic Hall | |
| voltage detection. Using simulated scans of the selected system parameters such | |
| as the polar angle $\theta$, magnetisation saturation | |
| ($\mu_\textrm{0}M_\textrm{s}$) or uniaxial magnetic anisotropy ($K_\textrm{u}$) | |
| we show the resultant changes in the harmonic Hall voltage, demonstrating the | |
| dominating influence of the $\mu_\textrm{0}M_\textrm{s}$ on the first and | |
| second harmonics. In the spin-diode ferromagnetic resonance (SD-FMR) technique | |
| resonance method the ($\mu_\textrm{0}M_\textrm{s}$, $K_\textrm{u}$) parameter | |
| space may be optimised numerically to obtain a set of viable curves that fit | |
| the experimental data.",2202.00364v1 | |
| 2022-02-03,Element Doping Enhanced Charge-to-Spin Conversion Efficiency in Amorphous PtSn4 Dirac Semimetal,"Topological semimetals (TSs) are promising candidates for low-power | |
| spin-orbit torque (SOT) devices due to their large charge-to-spin conversion | |
| efficiency. Here, we investigated the charge-to-spin conversion efficiency of | |
| amorphous PtSn4 (5 nm)/CoFeB (2.5-12.5 nm) layered structures prepared by a | |
| magnetron sputtering method at room temperature. The charge-to-spin ratio of | |
| PtSn4/CoFeB bilayers was 0.08, characterized by a spin torque ferromagnetic | |
| resonance (ST-FMR) technique. This ratio can further increase to 0.14 by | |
| inducing dopants, like Al and CoSi, into PtSn4. The dopants can also decrease | |
| (Al doping) or increase (CoSi doping) the resistivity of PtSn4. The work | |
| proposed a way to enhance the spin-orbit coupling (SOC) in amorphous TSs with | |
| dopants.",2202.01384v1 | |
| 2022-02-04,A Magnetoelectric Memory Device Based on Pseudo-Magnetization,"We propose a new type of magnetoelectric memory device that stores magnetic | |
| easy-axis information or pseudo-magnetization, rather than a definite | |
| magnetization direction, in piezoelectric/ferromagnetic (PE/FM) | |
| heterostructures. Theoretically, we show how a PE/FM combination can lead to | |
| non-volatility in pseudo-magnetization exhibiting ferroelectric-like behavior. | |
| The pseudo-magnetization can be manipulated by extremely low voltages | |
| especially when the FM is a low-barrier nanomagnet. Using a circuit model | |
| benchmarked against experiments, we determine the switching energy, delay, | |
| switching probability and retention time of the envisioned 1T/1C memory device | |
| in terms of magnetic and circuit parameters and discuss its thermal stability | |
| in terms of a key parameter called back-voltage vm which is an electrical | |
| measure of the strain-induced magnetic field. Taking advantage of ferromagnetic | |
| resonance (FMR) measurements, we experimentally extract values for vm in CoFeB | |
| films and circular nano-magnets deposited on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) | |
| which agree well with the theoretical values. Our experimental findings indeed | |
| indicate the feasibility of the proposed novel device and confirm the assumed | |
| parameters in our modeling effort.",2202.02203v2 | |
| 2016-03-09,Evolution of perpendicular magnetized tunnel junctions upon annealing,"We study the evolution of perpendicularly magnetized tunnel junctions under | |
| 300 to 400 $^{\circ}$C annealing. The hysteresis loops do not evolve much | |
| during annealing and they are not informative of the underlying structural | |
| evolutions. These evolutions are better revealed by the frequencies of the | |
| ferromagnetic resonance eigenmodes of the tunnel junction. Their modeling | |
| provides the exchange couplings and the layers' anisotropies within the stack | |
| which can serve as a diagnosis of the tunnel junction state after each | |
| annealing step. The anisotropies of the two CoFeB-based parts and the two | |
| Co/Pt-based parts of the tunnel junction decay at different rates during | |
| annealing. The ferromagnet exchange coupling through the texture-breaking Ta | |
| layer fails above 375$^{\circ}$C. The Ru spacer meant to promote a synthetic | |
| antiferromagnet behavior is also insufficiently robust to annealing. Based on | |
| these evolutions we propose optimization routes for the next generation tunnel | |
| junctions.",1603.02824v1 | |
| 2017-06-02,Dzyaloshinskii Moriya interaction across antiferromagnet / ferromagnet interface,"The antiferromagnet (AFM) / ferromagnet (FM) interfaces are of central | |
| importance in recently developed pure electric or ultrafast control of FM | |
| spins, where the underlying mechanisms remain unresolved. Here we report the | |
| direct observation of Dzyaloshinskii Moriya interaction (DMI) across the AFM/FM | |
| interface of IrMn/CoFeB thin films. The interfacial DMI is quantitatively | |
| measured from the asymmetric spin wave dispersion in the FM layer using | |
| Brillouin light scattering. The DMI strength is enhanced by a factor of 7 with | |
| increasing IrMn layer thickness in the range of 1- 7.5 nm. Our findings provide | |
| deeper insight into the coupling at AFM/FM interface and may stimulate new | |
| device concepts utilizing chiral spin textures such as magnetic skyrmions in | |
| AFM/FM heterostructures.",1706.00535v1 | |
| 2017-06-26,Enhancement of thermovoltage and tunnel magneto-Seebeck effect in CoFeB based magnetic tunnel junctions by variation of the MgAl$_2$O$_4$ and MgO barrier thickness,"We investigate the influence of the barrier thickness of | |
| Co$_{40}$Fe$_{40}$B$_{20}$ based magnetic tunnel junctions on the laser-induced | |
| tunnel magneto-Seebeck effect. Varying the barrier thickness from 1nm to 3nm, | |
| we find a distinct maximum in the tunnel magneto-Seebeck effect for 2.6nm | |
| barrier thickness. This maximum is independently measured for two barrier | |
| materials, namely MgAl$_2$O$_4$ and MgO. Additionally, samples with an | |
| MgAl$_2$O$_4$ barrier exhibit a high thermovoltage of more than 350$\mu$V in | |
| comparison to 90$\mu$V for the MTJs with MgO barrier when heated with the | |
| maximum laser power of 150mW. Our results allow for the fabrication of improved | |
| stacks when dealing with temperature differences across magnetic tunnel | |
| junctions for future applications in spin caloritronics, the emerging research | |
| field that combines spintronics and themoelectrics.",1706.08287v1 | |
| 2018-04-11,Broadband voltage rectifier induced by linear bias dependence in CoFeB/MgO magnetic tunnel junctions,"In this paper, the perpendicular magnetic anisotropy (PMA) is tailored by | |
| changing the thickness of the free layer with the objective of producing MTJ | |
| nano-pillars with smooth linear resistance dependence with both in-plane | |
| magnetic field and DC bias. We furthermore demonstrate how this linear bias | |
| dependence can be used to create a zero-threshold broadband voltage rectifier, | |
| a feature which is important for rectification in wireless charging and energy | |
| harvesting applications. By carefully balancing the amount of PMA acting in the | |
| free layer the measured RF to DC voltage conversion efficiency can be made as | |
| large as 11%.",1804.04104v1 | |
| 2018-04-14,Correlation between Dzyaloshinskii Moriya interaction and spin mixing conductance at antiferromagnet / ferromagnet interface,"The rich interaction phenomena at antiferromagnet (AFM)/ ferromagnet (FM) | |
| interfaces are key ingredients in AFM spintronics, where many underlying | |
| mechanisms remain unclear. Here we report a correlation observed between | |
| interfacial Dzyaloshinskii-Moriya interaction (DMI) Ds and effective spin | |
| mixing conductance g at IrMn/CoFeB interface. Both Ds and g are quantitatively | |
| determined with Brillouin light scattering measurements, and increase with IrMn | |
| thickness in the range of 2.5~7.5 nm. Such correlation likely originates from | |
| the AFM-states-mediated spin-flip transitions in FM, which promote both | |
| interfacial DMI and spin pumping effect. Our findings provide deeper insight | |
| into the AFM-FM interfacial coupling for future spintronic design.",1804.05151v2 | |
| 2018-04-18,Ferromagnetic resonance linewidth in coupled layers with easy-plane and perpendicular magnetic anisotropies,"Magnetic bilayers with different magnetic anisotropy directions are | |
| interesting for spintronic appli- cations as they offer the possibility to | |
| engineer tilted remnant magnetization states. We investigate the ferromagnetic | |
| resonance (FMR) linewidth of modes associated with two interlayer exchange- | |
| coupled ferromagnetic layers, the first a CoNi multilayer with a perpendicular | |
| magnetic anisotropy, and the second a CoFeB layer with an easy-plane | |
| anisotropy. For antiferromagnetic interlayer ex- change coupling, elevated FMR | |
| linewidths are observed below a characteristic field. This is in contrast to | |
| what is found in uncoupled, ferromagnetically coupled and single ferromagnetic | |
| layers in which the FMR linewidth increases monotonically with field. We show | |
| that the characteristic field at which there is a dramatic increase in FMR | |
| linewidth can be understood using a macrospin model with Heisenberg-type | |
| exchange coupling between the layers.",1804.06796v1 | |
| 2019-03-01,Individual skyrmion manipulation by local magnetic field gradients,"Magnetic skyrmions are topologically protected spin textures, stabilised in | |
| systems with strong Dzyaloshinskii-Moriya interaction (DMI). Several studies | |
| have shown that electrical currents can move skyrmions efficiently through | |
| spin-orbit torques. While promising for technological applications, | |
| current-driven skyrmion motion is intrinsically collective and accompanied by | |
| undesired heating effects. Here we demonstrate a new approach to control | |
| individual skyrmion positions precisely, which relies on the magnetic | |
| interaction between sample and a magnetic force microscopy (MFM) probe. We | |
| investigate perpendicularly magnetised X/CoFeB/MgO multilayers, where for X = W | |
| or Pt the DMI is sufficiently strong to allow for skyrmion nucleation in an | |
| applied field. We show that these skyrmions can be manipulated individually | |
| through the local field gradient generated by the scanning MFM probe with an | |
| unprecedented level of accuracy. Furthermore, we show that the probe stray | |
| field can assist skyrmion nucleation. Our proof-of-concepts results offer | |
| current-free paradigms to efficient individual skyrmion control.",1903.00367v1 | |
| 2019-03-04,Thermoelectric microscopy of magnetic skyrmions,"The magnetic skyrmion is a nanoscale topological object characterized by the | |
| winding of the magnetic moments, appearing in magnetic materials with broken | |
| inversion symmetry. Because of its low current threshold for driving, the | |
| skyrmions have been intensely studied toward novel storage applications by | |
| using electron-beam, X-ray, and visible light microscopies. Here, we show that | |
| the skyrmions can be imaged via thermoelectric signals of spin-caloritronic | |
| phenomena in combination with focused heating. We applied a local temperature | |
| gradient to a CoFeB/Ta/W multilayer film with scanning a heating position and, | |
| by exploiting a Hall bar structure, mapped the magnitude as well as the | |
| direction of the resultant thermoelectric current distributions, which link to | |
| skyrmions' inner magnetic textures. This method also enables the observation of | |
| skyrmion dynamics under driving current pulses, being a useful imaging | |
| technique for the development of skyrmion devices.",1903.01037v2 | |
| 2019-03-08,MFM and FORC+ study of switching mechanism in Co$_{25}$Pd$_{75}$ films,"Recent research on CoPd alloys with perpendicular magnetic anisotropy (PMA) | |
| has suggested that they might be useful as the pinning layer in CoFeB/MgO-based | |
| perpendicular magnetic tunnel junctions (pMTJ's) for various spintronic | |
| applications such as spin-torque transfer random access memory (STT-RAM). We | |
| have previously studied the effect of seed layer and composition on the | |
| structure (by XRD, SEM, AFM and TEM) and performance (coercivity) of these CoPd | |
| films. These films do not switch coherently, so the coercivity is determined by | |
| the details of the switching mechanism, which was not studied in our previous | |
| paper. In the present paper, we show that information can be obtained about the | |
| switching mechanism from magnetic force microscopy (MFM) together with first | |
| order reversal curves (FORC), despite the fact that MFM can only be used at | |
| zero field. We find that these films switch by a mechanism of domain nucleation | |
| and dendritic growth into a labyrinthine structure, after which the unreversed | |
| domains gradually shrink to small dots and then disappear.",1903.03568v2 | |
| 2020-03-26,Bipolar spin Hall nano-oscillators,"We demonstrate a novel type of spin Hall nano-oscillator (SHNO) that allows | |
| for efficient tuning of magnetic auto-oscillations over an extended range of | |
| gigahertz frequencies, using bipolar direct currents at constant magnetic | |
| fields. This is achieved by stacking two distinct ferromagnetic layers with a | |
| platinum interlayer. In this device, the orientation of the spin polarised | |
| electrons accumulated at the top and bottom interfaces of the platinum layer is | |
| switched upon changing the polarity of the direct current. As a result, the | |
| effective anti-damping required to drive large amplitude auto-oscillations can | |
| appear either at the top or bottom magnetic layer. Tuning of the | |
| auto-oscillation frequencies by several gigahertz can be obtained by combining | |
| two materials with sufficiently different saturation magnetization. Here we | |
| show that the combination of NiFe and CoFeB can result in 3 GHz shifts in the | |
| auto-oscillation frequencies. Bipolar SHNOs as such may bring enhanced | |
| synchronisation capabilities to neuromorphic computing applications.",2003.11776v1 | |
| 2020-06-02,Spin pumping and inverse spin Hall effect in iridium oxide,"Large charge-to-spin conversion (spin Hall angle) and spin Hall conductivity | |
| are prerequisites for development of next generation power efficient spintronic | |
| devices. In this context, heavy metals (e.g. Pt, W etc.), topological | |
| insulators, antiferromagnets are usually considered because they exhibit high | |
| spin-orbit coupling (SOC). In addition to the above materials, 5d transition | |
| metal oxide e.g. Iridium Oxide (IrO 2 ) is a potential candidate which exhibits | |
| high SOC strength. Here we report a study of spin pumping and inverse spin Hall | |
| effect (ISHE), via ferromagnetic resonance (FMR), in IrO 2 /CoFeB system. We | |
| identify the individual contribution of spin pumping and other spin | |
| rectification effects in the magnetic layer, by investigating the in-plane | |
| angular dependence of ISHE signal. Our analysis shows significant contribution | |
| of spin pumping effect to the ISHE signal. We show that polycrystalline IrO 2 | |
| thin film exhibits high spin Hall conductivity and spin Hall angle which are | |
| comparable to the values of Pt.",2006.01865v2 | |
| 2020-06-03,Giant voltage control of spin Hall nano-oscillator damping,"Spin Hall nano-oscillators (SHNOs) are emerging spintronic devices for | |
| microwave signal generation and oscillator based neuromorphic computing | |
| combining nano-scale footprint, fast and ultra-wide microwave frequency | |
| tunability, CMOS compatibility, and strong non-linear properties providing | |
| robust large-scale mutual synchronization in chains and two-dimensional arrays. | |
| While SHNOs can be tuned via magnetic fields and the drive current, neither | |
| approach is conducive for individual SHNO control in large arrays. Here, we | |
| demonstrate electrically gated W/CoFeB/MgO nano-constrictions in which the | |
| voltage-dependent perpendicular magnetic anisotropy, tunes the frequency and, | |
| thanks to nano-constriction geometry, drastically modifies the spin-wave | |
| localization in the constriction region resulting in a giant 42 % variation of | |
| the effective damping over four volts. As a consequence, the SHNO threshold | |
| current can be strongly tuned. Our demonstration adds key functionality to | |
| nano-constriction SHNOs and paves the way for energy-efficient control of | |
| individual oscillators in SHNO chains and arrays for neuromorphic computing.",2006.02151v1 | |
| 2020-07-04,Entropy-reduced retention times in magnetic memory elements: A case of the Meyer-Neldel Compensation Rule,"We compute mean waiting times between thermally-activated magnetization | |
| reversals in a nanodisk with parameters similar to a free CoFeB layer used in | |
| magnetic random access memories. By combining Langer's theory and forward flux | |
| sampling simulations, we show that the Arrhenius prefactor can take values up | |
| to 10$^{21}$ Hz, orders of magnitude beyond the value of 10$^{9}$ Hz typically | |
| assumed, and varies drastically as a function of material parameters. We show | |
| that the prefactor behaves like an exponential of the activation energy, which | |
| highlights a case of the Meyer-Neldel compensation rule. This suggests that | |
| modeling information retention times with a barrier-independent prefactor in | |
| such magnetic storage elements is not justified.",2007.02152v1 | |
| 2020-10-14,Spin torque gate magnetic field sensor,"Spin-orbit torque provides an efficient pathway to manipulate the magnetic | |
| state and magnetization dynamics of magnetic materials, which is crucial for | |
| energy-efficient operation of a variety of spintronic devices such as magnetic | |
| memory, logic, oscillator, and neuromorphic computing. Here, we describe and | |
| experimentally demonstrate a strategy for the realization of a spin torque gate | |
| magnetic field sensor with extremely simple structure by exploiting the | |
| longitudinal field dependence of the spin torque driven magnetization | |
| switching. Unlike most magnetoresistance sensors which require a delicate | |
| magnetic bias to achieve a linear response to the external field, the spin | |
| torque gate sensor can achieve the same without any magnetic bias, which | |
| greatly simplifies the sensor structure. Furthermore, by driving the sensor | |
| using an ac current, the dc offset is automatically suppressed, which | |
| eliminates the need for a bridge or compensation circuit. We verify the concept | |
| using the newly developed WTe2/Ti/CoFeB trilayer and demonstrate that the | |
| sensor can work linearly in the range of 3-10 Oe with negligible dc offset.",2010.07158v1 | |
| 2020-11-06,Picosecond Switching of Optomagnetic Tunnel Junctions,"Perpendicular magnetic tunnel junctions are one of the building blocks for | |
| spintronic memories, which allow fast nonvolatile data access, offering | |
| substantial potentials to revolutionize the mainstream computing architecture. | |
| However, conventional switching mechanisms of such devices are fundamentally | |
| hindered by spin polarized currents4, either spin transfer torque or spin orbit | |
| torque with spin precession time limitation and excessive power dissipation. | |
| These physical constraints significantly stimulate the advancement of modern | |
| spintronics. Here, we report an optomagnetic tunnel junction using a | |
| spintronic-photonic combination. This composite device incorporates an | |
| all-optically switchable Co/Gd bilayer coupled to a CoFeB/MgO-based | |
| perpendicular magnetic tunnel junction by the Ruderman-Kittel-Kasuya-Yosida | |
| interaction. A picosecond all-optical operation of the optomagnetic tunnel | |
| junction is explicitly confirmed by time-resolved measurements. Moreover, the | |
| device shows a considerable tunnel magnetoresistance and thermal stability. | |
| This proof-of-concept device represents an essential step towards ultrafast | |
| spintronic memories with THz data access, as well as ultralow power | |
| consumption.",2011.03612v1 | |
| 2020-12-10,Observation of Magnetic Droplets in Magnetic Tunnel Junctions,"Magnetic droplets, a class of highly non-linear magnetodynamical solitons, | |
| can be nucleated and stabilized in nanocontact spin-torque nano-oscillators | |
| where they greatly increase the microwave output power. Here, we experimentally | |
| demonstrate magnetic droplets in magnetic tunnel junctions (MTJs). The droplet | |
| nucleation is accompanied by a power increase of over 300 times compared to its | |
| ferromagnetic resonance modes. The nucleation and stabilization of droplets are | |
| ascribed to the double-CoFeB free layer structure in the all-perpendicular MTJ | |
| which provides a low Zhang-Li torque and a high pinning field. Our results | |
| enable better electrical sensitivity in the fundamental studies of droplets and | |
| show that the droplets can be utilized in MTJ-based applications.",2012.05596v1 | |
| 2020-12-20,Creation of a Chiral Bobber Lattice in Helimagnet-Multilayer Heterostructures,"A chiral bobber is a localized three-dimensional magnetization configuration, | |
| terminated by a singularity. Chiral bobbers coexist with magnetic skyrmions in | |
| chiral magnets, lending themselves to new types of skyrmion-complementary bits | |
| of information. However, the on-demand creation of bobbers, as well as their | |
| direct observation remained elusive. Here, we introduce a new mechanism for | |
| creating a stable chiral bobber lattice state via the proximity of two skyrmion | |
| species with comparable size. This effect is experimentally demonstrated in a | |
| Cu$_2$OSeO$_3$/[Ta/CoFeB/MgO]$_4$ heterostructure in which an exotic bobber | |
| lattice state emerges in the phase diagram of Cu$_2$OSeO$_3$. To unambiguously | |
| reveal the existence of the chiral bobber lattice state, we have developed a | |
| novel characterization technique, magnetic truncation rod analysis, which is | |
| based on resonant elastic x-ray scattering.",2012.10924v1 | |
| 2021-01-10,A Thermodynamic Core using Voltage-Controlled Spin-Orbit-Torque Magnetic Tunnel Junctions,"We present a magnetic implementation of a thermodynamic computing fabric. | |
| Magnetic devices within computing cores harness thermodynamics through its | |
| voltage-controlled thermal stability; while the evolution of network states is | |
| guided by the spin-orbit-torque effect. We theoretically derive the dynamics of | |
| the cores and show that the computing fabric can successfully compute ground | |
| states of a Boltzmann Machine. Subsequently, we demonstrate the physical | |
| realization of these devices based on a CoFeB-MgO magnetic tunnel junction | |
| structure. The results of this work pave the path towards the realization of | |
| highly efficient, high-performance thermodynamic computing hardware. Finally, | |
| this paper will also give a perspective of computing beyond thermodynamic | |
| computing.",2101.03448v3 | |
| 2021-04-07,Magnetic Reversal and Critical Current Transparency of CoFeB Superconductor-Ferromagnet-Superconductor Heterostructures,"In this work, we show fundamental low temperature (T) magnetic and Ic | |
| responses of a magnetic Josephson Junction (MJJ) S/F/S heterostructure - Nb/ | |
| Co56Fe24B20 /Nb. The ultra-thin Co56Fe24B20 (CFB) films (0.6-1.3 nm) were | |
| deposited onto two separate buffer layers: 150 nm Nb/5 nm Cu and 150 nm Nb/ (1 | |
| nm Cu/0.5 nm Nb)6/1 nm Cu. Both film sets were capped with 5 nm Cu/50 nm Nb. | |
| Magnetic results show reduced switching distributions in patterned arrays | |
| measured at near liquid Helium temperature (~ 10 K), with the incorporation of | |
| the (1 nm Cu/0.5 nm Nb)6/1 nm multilayer. In electrical devices, the critical | |
| current (Ic) through the CFB layer decays exponentially with increasing | |
| ferromagnetic layer thickness and shows a dip in Ic at 0.8 nm, characteristic | |
| of a change in the equilibrium Josephson phase in an S/F/S structure.",2104.03188v1 | |
| 2021-06-22,Room And Cryogenic Temperature Behaviour of Magnetic Sensors Based on Gan/Si Single Saw Resonators,"This work analyzes resonance frequency shift vs. the applied magnetic field | |
| strength for GHz operating GaN/Si SAW single resonators. Magnetostrictive | |
| elements (Ni and CoFeB) were deposited in the proximity of the interdigitated | |
| transducers (IDTs) of the resonators (A-type structures) and also over the | |
| IDTs, after covering them with a BCB layer to avoid short circuits with IDTs | |
| metal (B-type structures). This work targets emerging applications of SAW | |
| resonators in driving spin wave pumping and in coupling of surface acoustic | |
| waves (SAW) with superconducting Q-bits. Magnetic sensitivity of the SAWs was | |
| analyzed at room temperature (RT) and at cryogenic temperatures, obtaining high | |
| magnetic sensitivities at 16 K. According to our knowledge, GaN based SAWs are | |
| first time used in magnetic applications; also, cryogenic behavior of magnetic | |
| SAW sensors is first time analyzed.",2106.11605v1 | |
| 2021-08-01,Terahertz charge and spin transport in metallic ferromagnets: the role of crystalline and magnetic order,"We study the charge and spin dependent scattering in a set of CoFeB thin | |
| films whose crystalline order is systematically enhanced and controlled by | |
| annealing at increasingly higher temperatures. Terahertz conductivity | |
| measurements reveal that charge transport closely follows the development of | |
| the crystalline phase, with increasing structural order leading to higher | |
| conductivity. The terahertz-induced ultrafast demagnetization, driven by | |
| spin-flip scattering mediated by the spin-orbit interaction, is measurable in | |
| the pristine amorphous sample and much reduced in the sample with highest | |
| crystalline order. Surprisingly, the largest demagnetization is observed at | |
| intermediate annealing temperatures, where the enhancement in spin-flip | |
| probability is not associated with an increased charge scattering. We are able | |
| to correlate the demagnetization amplitude with the magnitude of the in-plane | |
| magnetic anisotropy, which we characterize independently, suggesting a | |
| magnetoresistance-like description of the phenomenon.",2108.00456v1 | |
| 2021-11-12,Fabrication of voltage gated spin Hall nano-oscillators,"We demonstrate an optimized fabrication process for electric field (voltage | |
| gate) controlled nano-constriction spin Hall nano-oscillators (SHNOs), | |
| achieving feature sizes of <30 nm with easy to handle ma-N 2401 e-beam | |
| lithography negative tone resist. For the nanoscopic voltage gates, we utilize | |
| a two-step tilted ion beam etching approach and through-hole encapsulation | |
| using 30 nm HfO<sub>x</sub>. The optimized tilted etching process reduces | |
| sidewalls by 75% compared to no tilting. Moreover, the HfO<sub>x</sub> | |
| encapsulation avoids any sidewall shunting and improves gate breakdown. Our | |
| experimental results on W/CoFeB/MgO/SiO<sub>2</sub> SHNOs show significant | |
| frequency tunability (6 MHz/V) even for moderate perpendicular magnetic | |
| anisotropy. Circular patterns with diameter of 45 nm are achieved with an | |
| aspect ratio better than 0.85 for 80% of the population. The optimized | |
| fabrication process allows incorporating a large number of individual gates to | |
| interface to SHNO arrays for unconventional computing and densely packed | |
| spintronic neural networks.",2111.06957v1 | |
| 2021-11-26,Three-dimensional Resonant Magnetization Dynamics Unraveled by Time-Resolved Soft X-ray Laminography,"The imaging of magneto-dynamical processes has been, so far, mostly a | |
| two-dimensional business, due to the constraints of the available experimental | |
| techniques. In this manuscript, building on the recent developments of soft | |
| X-ray magnetic laminography, we present an experimental setup where | |
| magneto-dynamical processes can be resolved in all three spatial dimensions and | |
| in time, with the possibility to freely tune the frequency of the dynamical | |
| process. We then employ this setup to investigate the three-dimensional | |
| dynamics of two resonant magneto-dynamical modes in a CoFeB microstructure | |
| occurring at different frequencies, namely the fundamental vortex gyration mode | |
| and a magnetic field-induced domain wall excitation mode. This new technique | |
| provides much needed capabilities for the experimental investigation of the | |
| magnetization dynamics of three-dimensional magnetic systems.",2111.13533v1 | |
| 2022-01-11,Perpendicular magnetic tunnel junctions with multi-interface free layer,"Future generations of magnetic random access memory demand magnetic tunnel | |
| junctions that can provide simultaneously high magnetoresistance, strong | |
| retention, low switching energy and small cell size below 10nm. Here we study | |
| perpendicular magnetic tunnel junctions with composite free layers where | |
| multiple ferromagnet/nonmagnet interfaces can contribute to the thermal | |
| stability. Different nonmagnetic materials (MgO, Ta, Mo) have been employed as | |
| the coupling layers in these multi-interface free layers. The evolution of | |
| junction properties under different annealing conditions is investigated. A | |
| strong dependence of tunneling magnetoresistance on the thickness of the first | |
| CoFeB layer has been observed. In junctions where Mo and MgO are used as | |
| coupling layers, large tunneling magnetoresistance above 200% has been achieved | |
| after 400{\deg}C annealing.",2201.03798v1 | |
| 2022-04-06,Power transfer in magnetoelectric resonators,"We derive an analytical model for the power transfer in a magnetoelectric | |
| film bulk acoustic resonator consisting of a piezoelectric--magnetostrictive | |
| bilayer. The model describes the dynamic magnetostrictive influence on the | |
| elastodynamics via an effective frequency-dependent stiffness constant. This | |
| allows for the calculation of both the magnetic and elastic power absorption in | |
| the resonator as well as of its energy efficiency when such a resonator is | |
| considered as a magnetic transducer. The model is then applied to example | |
| systems consisting of piezoelectric ScAlN and magnetostrictive CoFeB, Ni, or | |
| Terfenol-D layers.",2204.03072v2 | |
| 2022-10-03,"Voltage control of frequency, effective damping and threshold current in nano-constriction-based spin Hall nano-oscillators","Using micromagnetic simulations, we study the interplay between strongly | |
| voltage-controlled magnetic anisotropy (VCMA), $\Delta K = \pm$200 kJ/m$^3$, | |
| and gate width, $w=$ 10--400 nm, in voltage-gated W/CoFeB/MgO based | |
| nano-constriction spin Hall nano-oscillators. The VCMA modifies the local | |
| magnetic properties such that the magnetodynamics transitions between regimes | |
| of \emph{i}) confinement, \emph{ii}) tuning, and \emph{iii}) separation, with | |
| qualitatively different behavior. We find that the strongest tuning is achieved | |
| for gate widths of the same size as the the constriction width, for which the | |
| effective damping can be increased an order of magnitude compared to its | |
| intrinsic value. As a consequence, voltage control remains efficient over a | |
| very large frequency range, and subsequent manufacturing advances could allow | |
| SHNOs to be easily integrated into next-generation electronics for further | |
| fundamental studies and industrial applications.",2210.01042v1 | |
| 2022-10-11,Thermally-generated spin current in the topological insulator Bi$_2$Se$_3$,"We complete measurements of interconversions among the full triad of thermal | |
| gradients, charge currents, and spin currents in the topological insulator | |
| Bi$_2$Se$_3$ by quantifying the efficiency with which thermal gradients can | |
| generate transverse spin currents. We accomplish this by comparing the spin | |
| Nernst magneto-thermopower to the spin Hall magnesistance for bilayers of | |
| Bi$_2$Se$_3$/CoFeB. We find that Bi$_2$Se$_3$ does generate substantial | |
| thermally-driven spin currents. A lower bound for the ratio of spin current to | |
| thermal gradient is $J_s/\nabla_x T$ = (4.9 $\pm$ 0.9) $\times$ 10$^{6}$ | |
| ($\hbar/2e$) A m$^{-2}$ / K $\mu$m$^{-1}$, and a lower bound for the magnitude | |
| of the spin Nernst ratio is $-$0.61 $\pm$ 0.11. The spin Nernst ratio for | |
| Bi$_2$Se$_3$ is the largest among all materials measured to date, 2-3 times | |
| larger compared to previous measurements for the heavy metals Pt and W.",2210.05636v1 | |
| 2022-10-26,"Perpendicular magnetic anisotropy, tunneling magnetoresistance and spin-transfer torque effect in magnetic tunnel junctions with Nb layers","Nb and its compounds are widely used in quantum computing due to their high | |
| superconducting transition temperatures and high critical fields. Devices that | |
| combine superconducting performance and spintronic non-volatility could deliver | |
| unique functionality. Here we report the study of magnetic tunnel junctions | |
| with Nb as the heavy metal layers. An interfacial perpendicular magnetic | |
| anisotropy energy density of 1.85 mJ/m2 was obtained in Nb/CoFeB/MgO | |
| heterostructures. The tunneling magnetoresistance was evaluated in junctions | |
| with different thickness combinations and different annealing conditions. An | |
| optimized magnetoresistance of 120% was obtained at room temperature, with a | |
| damping parameter of 0.011 determined by ferromagnetic resonance. In addition, | |
| spin-transfer torque switching has also been successfully observed in these | |
| junctions with a quasistatic switching current density of 7.3*10^5 A/cm2.",2210.14969v1 | |
| 2022-10-30,"Interplay of symmetry-conserved tunneling, interfacial oxidation and perpendicular magnetic anisotropy in CoFeB/MgO-based junctions","The interfacial oxidation level and thermodynamic properties of the MgO-based | |
| perpendicular magnetic tunneling junctions are investigated. The | |
| symmetry-conserved tunneling effect depends sensitively on the MgO adatom | |
| energy during the RF sputtering, as well as the thermal stability of the | |
| structure during the post-growth thermal annealing. Two different failure modes | |
| of the magnetoresistance are highlighted, involving with the decay of | |
| perpendicular magnetic anisotropy and destruction of coherent tunneling | |
| channels, respectively. Through the careful control of interfacial oxidation | |
| level and proper selection of the heavy metal layers, both perpendicular | |
| magnetic anisotropy and tunneling magnetoresistance of the junctions can be | |
| increased.",2210.16734v1 | |
| 2022-12-08,Acoustic-Driven Magnetic Skyrmion Motion,"Magnetic skyrmions have great potential for developing novel spintronic | |
| devices. The electrical manipulation of skyrmions has mainly relied on | |
| current-induced spin-orbit torques. A recent theoretical model suggested that | |
| the skyrmions could be more efficiently manipulated by surface acoustic waves | |
| (SAW), an elastic wave that can couple with magnetic moment through | |
| magnetoelastic effect. However, the directional motion of skyrmions that is | |
| driven by SAW is still missing. Here, we experimentally demonstrate the motion | |
| of N\'eel-type skyrmions in Ta/CoFeB/MgO/Ta multilayers driven by propagating | |
| SAW pulses from on-chip piezoelectric transducers. Our results reveal that the | |
| elastic wave with longitudinal and shear vertical displacements (Rayleigh wave) | |
| traps skyrmions, while the shear horizontal wave effectively drives the motion | |
| of skyrmions. In particular, a longitudinal motion along the SAW propagation | |
| direction and a transverse motion due to topological charge, are observed and | |
| further confirmed by our micromagnetic simulations. This work demonstrates a | |
| promising approach based on acoustic waves for manipulating skyrmions, which | |
| could offer new opportunities for ultra-low power spintronics.",2212.04049v1 | |
| 2023-04-30,Specific features of g $\approx$ 4.3 EPR line behavior in magnetic nanogranular composites,"Films of metal-insulator nanogranular composites M$_x$D$_{100-x}$ with | |
| different composition and percentage of metal and dielectric phases (M = Fe, | |
| Co, CoFeB; D = Al$_2$O$_3$, SiO$_2$, LiNbO$_3$; x $\approx$ 15-70 at.%) are | |
| investigated by magnetic resonance in a wide range of frequencies (f = 7-37 | |
| GHz) and temperatures (T = 4.2-360 K). In addition to the usual ferromagnetic | |
| resonance signal from an array of nanogranules, the experimental spectra | |
| contain an additional absorption peak, which we associate with the electron | |
| paramagnetic resonance (EPR) of Fe and Co ions dispersed in the insulating | |
| space between the granules. In contrast to the traditional EPR of Fe and Co | |
| ions in weakly doped non-magnetic matrices, the observed peak demonstrates a | |
| number of unusual properties, which we explain by the presence of magnetic | |
| interactions between ions and granules.",2305.00551v1 | |
| 2023-05-16,Terahertz spin conductance probes of coherent and incoherent spin tunneling through MgO tunnel junctions,"We study femtosecond spin currents through MgO tunneling barriers in CoFeB(2 | |
| nm)|MgO($d$)|Pt(2 nm) stacks by terahertz emission spectroscopy. To obtain | |
| transport information independent of extrinsic experimental factors, we | |
| determine the complex-valued spin conductance $\tilde{G}_d (\omega)$ of the MgO | |
| layer (thickness d= 0-6 {\AA} over a wide frequency range $(\omega/2\pi=$ 0.5-8 | |
| THz). In the time $(t)$ domain,$ G_d (t)$ has an instantaneous and delayed | |
| component that point to (i) spin transport through Pt pinholes in MgO, (ii) | |
| coherent spin tunneling and (iii) incoherent resonant spin tunneling mediated | |
| by defect states in MgO. A remarkable signature of (iii) is its relaxation time | |
| that grows monotonically with $d$ to as much as 270 fs at $d= 6$ {\AA}, in full | |
| agreement with an analytical model. Our results indicate that terahertz spin | |
| conductance spectroscopy will yield new and relevant insights into ultrafast | |
| spin transport for a wide range of materials.",2305.09074v2 | |
| 2023-05-18,Observation and enhancement of room temperature bilinear magnetoelectric resistance in sputtered topological semimetal Pt3Sn,"Topological semimetal materials have become a research hotspot due to their | |
| intrinsic strong spin-orbit coupling which leads to large charge-to-spin | |
| conversion efficiency and novel transport behaviors. In this work, we have | |
| observed a bilinear magnetoelectric resistance (BMER) of up to 0.1 nm2A-1Oe-1 | |
| in a singlelayer of sputtered semimetal Pt3Sn at room temperature. Different | |
| from previous observations, the value of BMER in sputtered Pt3Sn does not | |
| change out-of-plane due to the polycrystalline nature of Pt3Sn. The observation | |
| of BMER provides strong evidence of the existence of spin-momentum locking in | |
| the sputtered polycrystalline Pt3Sn. By adding an adjacent CoFeB magnetic | |
| layer, the BMER value of this bilayer system is doubled compared to the single | |
| Pt3Sn layer. This work broadens the material system in BMER study, which paves | |
| the way for the characterization of topological states and applications for | |
| spin memory and logic devices.",2305.10720v2 | |
| 2023-07-07,Orbitronics: Light-induced Orbit Currents in Terahertz Emission Experiments,"Orbitronics is based on the use of orbit currents as information carriers. Up | |
| to now, orbit currents were created from the conversion of charge or spin | |
| currents, and inversely, they could be converted back to charge or spin | |
| currents. Here we demonstrate that orbit currents can also be generated by | |
| femtosecond light pulses on Ni. In multilayers associating Ni with oxides and | |
| nonmagnetic metals such as Cu, we detect the orbit currents by their conversion | |
| into charge currents and the resulting terahertz emission. We show that the | |
| orbit currents extraordinarily predominate the light-induced spin currents in | |
| Ni-based systems, whereas only spin currents can be detected with CoFeB-based | |
| systems. In addition, the analysis of the time delays of the terahertz pulses | |
| leads to relevant information on the velocity and propagation of orbit | |
| carriers. Our finding of light-induced orbit currents and our observation of | |
| their conversion into charge currents opens new avenues in orbitronics, | |
| including the development of orbitronic terahertz devices.",2307.03490v1 | |
| 2023-09-06,Shaping magnetization dynamics in a planar square dot by adjusting its surface anisotropy,"A planar square dot is one of the simplest structures confined to three | |
| dimensions. Despite its geometrical simplicity, the description of the spin | |
| wave modes in this structure is not trivial due to the competition of dipolar | |
| and exchange interactions. An additional factor that makes this description | |
| challenging are the boundary conditions depend both on non-local dipolar | |
| interactions and local surface parameters such as surface anisotropy. In the | |
| presented work, we showed how the surface anisotropy applied at the lateral | |
| faces of the dot can tune the frequency of fundamental mode in the planar CoFeB | |
| dot, magnetized in an out-of-plane direction. Moreover, we analyzed the spin | |
| wave profile of the fundamental mode and the corresponding dynamic stray field. | |
| We showed that the asymmetric application of surface anisotropy produces an | |
| asymmetric profile of dynamic stray field for square dot and can be used to | |
| tailor inter-dot coupling. The calculations were performed with the use of the | |
| finite-element method.",2309.02984v1 | |
| 2023-09-22,Strongly Coupled Spin Waves and Surface Acoustic Waves at Room Temperature,"Here, we report the observation of strong coupling between magnons and | |
| surface acoustic wave (SAW) phonons in a thin CoFeB film constructed in an | |
| on-chip SAW resonator by analyzing SAW phonon dispersion anticrossings. Our | |
| device design provides the tunability of the film thickness with a fixed phonon | |
| wavelength, which is a departure from the conventional approach in strong | |
| magnon--phonon coupling research. We detect a monotonic increase in the | |
| coupling strength by expanding the film thickness, which agrees with our | |
| theoretical model. Our work offers a significant way to advance fundamental | |
| research and the development of devices based on magnon--phonon hybrid | |
| quasiparticles.",2309.12690v1 | |
| 2023-10-20,Visualization of skyrmion-superconducting vortex pairs in a chiral magnet-superconductor heterostructure,"Magnetic skyrmions, the topological states possessing chiral magnetic | |
| structure with non-trivial topology, have been widely investigated as a | |
| promising candidate for spintronic devices. They can also couple with | |
| superconducting vortices to form skyrmion-vortex pairs, hosting Majorana zero | |
| mode which is a potential candidate for topological quantum computering. A lot | |
| of theoretical proposals have been put forward on constructing skyrmion-vortex | |
| pairs in heterostructures of chiral magnet and superconductor. Nevertheless, | |
| how to generate skyrmion-vortex pairs in a controllable way experimentally | |
| remains a significant challenge. We have designed a heterostructure of chiral | |
| magnet and superconductor [CoFeB/Ir/Ta]7/Nb in which zero field N\'eel-type | |
| skyrmions can be stabilized and the superconducting vortices can couple with | |
| the skyrmions when Nb is in the superconducting state. We have directly | |
| observed the formation of skyrmion-superconducting vortex pairs which is | |
| dependent on the direction of the applied magnetic field. Our results provide | |
| an effective method to manipulate the quantum states of skyrmions with the help | |
| of superconducting vortices, which can be used to explore the possible | |
| existence of Majorana zero mode for future quantum computation.",2310.13363v1 | |
| 2023-10-26,On-chip all-electrical determination of the magnetoelastic coupling constant of magnetic heterostructures,"We have developed an approach to determine the magnetoelastic coupling | |
| constant of magnetic layers in thin film heterostructures. The film is formed | |
| on a piezoelectric substrate between two interdigital transducers (IDT), a | |
| platform often used to construct a surface acoustic wave device. With the | |
| substrate piezoelectricity, strain is induced into the film by applying a dc | |
| voltage to the IDTs. The strain causes changes in the magnetization direction | |
| of the magnetic layer, which is probed by measuring changes, if any, in the | |
| transverse resistance of the heterostructure. We find the extracted | |
| magnetoelastic coupling constant of the magnetic layer (CoFeB) depends on the | |
| film stacking. Such change can be accounted for provided that the elastic | |
| properties of the layers that constitute the heterostructures are taken into | |
| account. The on-chip all-electrical approach described here provides a | |
| versatile means to quantitatively assess the magnetoelastic coupling constant | |
| of thin film heterostructures.",2310.17215v1 | |
| 2023-12-06,Large Non-Volatile Frequency Tuning of Spin Hall Nano-Oscillators using Circular Memristive Nano-Gates,"Spin Hall nano oscillators (SHNOs) are promising candidates for neuromorphic | |
| computing due to their miniaturized dimensions, non-linearity, fast dynamics, | |
| and ability to synchronize in long chains and arrays. However, tuning the | |
| individual SHNOs in large chains/arrays, which is key to implementing synaptic | |
| control, has remained a challenge. Here, we demonstrate circular memristive | |
| nano-gates, both precisely aligned and shifted with respect to | |
| nano-constriction SHNOs of W/CoFeB/HfOx, with increased quality of the device | |
| tunability. Gating at the exact center of the nano-constriction region is found | |
| to cause irreversible degradation to the oxide layer, resulting in a permanent | |
| frequency shift of the auto-oscillating modes. As a remedy, gates shifted | |
| outside of the immediate nano-constriction region can tune the frequency | |
| dramatically (>200 MHz) without causing any permanent change to the | |
| constriction region. Circular memristive nano-gates can, therefore, be used in | |
| SHNO chains/arrays to manipulate the synchronization states precisely over | |
| large networks of oscillators.",2312.03352v2 | |
| 2008-05-16,The influence of intergranular interaction on the magnetization of the ensemble of oriented Stoner-Wohlfarth nanoparticles,"We consider the influence of interparticle interaction on the magnetization | |
| reversal in the oriented Stoner-Wohlfarth nanoparticles ensemble. To do so, we | |
| solve a kinetic equation for the relaxation of the overall ensemble | |
| magnetization to its equilibrium value in some effective mean field. Latter | |
| field consists of external magnetic field and interaction mean field | |
| proportional to the instantaneous value of above magnetization. We show that | |
| the interparticle interaction influences the temperature dependence of a | |
| coercive field. This influence manifests itself in the noticeable coercivity at | |
| $T>T_{b}$ ($T_{b}$ is so-called blocking temperature). The above interaction | |
| can also lead to a formation of the ""superferromagnetic"" state with correlated | |
| directions of particle magnetic moments at $T>T_{b}$. This state possesses | |
| coercivity if the overall magnetization has a component directed along the easy | |
| axis of each particle. We have shown that the coercive field in the | |
| ""superferromagnetic"" state does not depend on measuring time. This time | |
| influences both $T_{b}$ and the temperature dependence of coercive field at | |
| $T<T_{b}$. We corroborate our theoretical results by measurements on | |
| nanogranular films (CoFeB)$_{x}$-(SiO$_{2}$)$_{1-x}$ with concentration of | |
| ferromagnetic particles close, but below percolation threshold.",0805.2463v3 | |
| 2009-07-22,Quantized spin wave modes in magnetic tunnel junction nanopillars,"We present an experimental and theoretical study of the magnetic field | |
| dependence of the mode frequency of thermally excited spin waves in rectangular | |
| shaped nanopillars of lateral sizes 60x100, 75x150, and 105x190 nm2, patterned | |
| from MgO-based magnetic tunnel junctions. The spin wave frequencies were | |
| measured using spectrally resolved electrical noise measurements. In all | |
| spectra, several independent quantized spin wave modes have been observed and | |
| could be identified as eigenexcitations of the free layer and of the synthetic | |
| antiferromagnet of the junction. Using a theoretical approach based on the | |
| diagonalization of the dynamical matrix of a system of three coupled, spatially | |
| confined magnetic layers, we have modeled the spectra for the smallest pillar | |
| and have extracted its material parameters. The magnetization and exchange | |
| stiffness constant of the CoFeB free layer are thereby found to be | |
| substantially reduced compared to the corresponding thin film values. Moreover, | |
| we could infer that the pinning of the magnetization at the lateral boundaries | |
| must be weak. Finally, the interlayer dipolar coupling between the free layer | |
| and the synthetic antiferromagnet causes mode anticrossings with gap openings | |
| up to 2 GHz. At low fields and in the larger pillars, there is clear evidence | |
| for strong non-uniformities of the layer magnetizations. In particular, at zero | |
| field the lowest mode is not the fundamental mode, but a mode most likely | |
| localized near the layer edges.",0907.3792v2 | |
| 2014-09-02,Switching of Perpendicularly Polarized Nanomagnets with Spin Orbit Torque without an External Magnetic Field by Engineering a Tilted Anisotropy,"Spin orbit torque (SOT) provides an efficient way of generating spin current | |
| that promises to significantly reduce the current required for switching | |
| nanomagnets. However, an in-plane current generated SOT cannot | |
| deterministically switch a perpendicularly polarized magnet due to symmetry | |
| reasons. On the other hand, perpendicularly polarized magnets are preferred | |
| over in-plane magnets for high-density data storage applications due to their | |
| significantly larger thermal stability in ultra-scaled dimensions. Here we show | |
| that it is possible switch a perpendicularly polarized magnet by SOT without | |
| needing an external magnetic field. This is accomplished by engineering an | |
| anisotropy in the magnets such that the magnetic easy axis slightly tilts away | |
| from the film-normal. Such a tilted anisotropy breaks the symmetry of the | |
| problem and makes it possible to switch the magnet deterministically. Using a | |
| simple Ta/CoFeB/MgO/Ta heterostructure, we demonstrate reversible switching of | |
| the magnetization by reversing the polarity of the applied current. This | |
| demonstration presents a new approach for controlling nanomagnets with spin | |
| orbit torque.",1409.0620v3 | |
| 2015-10-13,Efficient metallic spintronic emitters of ultrabroadband terahertz radiation,"Terahertz electromagnetic radiation is extremely useful for numerous | |
| applications such as imaging and spectroscopy. Therefore, it is highly | |
| desirable to have an efficient table-top emitter covering the 1-to-30-THz | |
| window whilst being driven by a low-cost, low-power femtosecond laser | |
| oscillator. So far, all solid-state emitters solely exploit physics related to | |
| the electron charge and deliver emission spectra with substantial gaps. Here, | |
| we take advantage of the electron spin to realize a conceptually new terahertz | |
| source which relies on tailored fundamental spintronic and photonic phenomena | |
| in magnetic metal multilayers: ultrafast photo-induced spin currents, the | |
| inverse spin-Hall effect and a broadband Fabry-P\'erot resonance. Guided by an | |
| analytical model, such spintronic route offers unique possibilities for | |
| systematic optimization. We find that a 5.8-nm-thick W/CoFeB/Pt trilayer | |
| generates ultrashort pulses fully covering the 1-to-30-THz range. Our novel | |
| source outperforms laser-oscillator-driven emitters such as ZnTe(110) crystals | |
| in terms of bandwidth, terahertz-field amplitude, flexibility, scalability and | |
| cost.",1510.03729v2 | |
| 2016-07-22,The Spin Nernst effect in Tungsten,"The spin Hall effect allows generation of spin current when charge current is | |
| passed along materials with large spin orbit coupling. It has been recently | |
| predicted that heat current in a non-magnetic metal can be converted into spin | |
| current via a process referred to as the spin Nernst effect. Here we report the | |
| observation of the spin Nernst effect in W. In W/CoFeB/MgO heterostructures, we | |
| find changes in the longitudinal and transverse voltages with magnetic field | |
| when temperature gradient is applied across the film. The field-dependence of | |
| the voltage resembles that of the spin Hall magnetoresistance. A comparison of | |
| the temperature gradient induced voltage and the spin Hall magnetoresistance | |
| allows direct estimation of the spin Nernst angle. We find the spin Nernst | |
| angle of W to be similar in magnitude but opposite in sign with its spin Hall | |
| angle. Interestingly, under an open circuit condition, such sign difference | |
| results in spin current generation larger than otherwise. These results | |
| highlight the distinct characteristics of the spin Nernst and spin Hall | |
| effects, providing pathways to explore materials with unique band structures | |
| that may generate large spin current with high efficiency.",1607.06594v2 | |
| 2017-09-08,Observation of Magnetic Radial Vortex Nucleation in a Multilayer Stack with Tunable Anisotropy,"Recently discovered exotic magnetic configurations, namely magnetic solitons | |
| appearing in the presence of bulk or interfacial Dzyaloshinskii-Moriya | |
| Interaction (i-DMI), have excited scientists to explore their potential | |
| applications in emerging spintronic technologies such as race-track magnetic | |
| memory, spin logic, radio frequency nano-oscillators and sensors. Such studies | |
| are motivated by their foreseeable advantages over conventional micro-magnetic | |
| structures due to their small size, topological stability and easy spin-torque | |
| driven manipulation with much lower threshold current densities giving way to | |
| improved storage capacity, and faster operation with efficient use of energy. | |
| In this work, we show that in the presence of i-DMI in Pt/CoFeB/Ti multilayers | |
| by tuning the magnetic anisotropy (both in-plane and perpendicular-to-plane) | |
| via interface engineering and postproduction treatments, we can stabilize a | |
| variety of magnetic configurations such as N\'eel skyrmions, horseshoes and | |
| most importantly for the first time, the recently predicted isolated radial | |
| vortices at room temperature and under zero bias field. Especially, the radial | |
| vortex state with its absolute convergence to or divergence from a single point | |
| can potentially offer exciting new applications such as particle | |
| trapping/detrapping in addition to magnetoresistive memories with efficient | |
| switching, where the radial vortex state can act as a source of spin-polarized | |
| current with radial polarization.",1709.02876v1 | |
| 2018-03-12,Electrical initialization of electron and nuclear spins in a single quantum dot at zero magnetic field,"The emission of circularly polarized light from a single quantum dot relies | |
| on the injection of carriers with well-defined spin polarization. Here we | |
| demonstrate single dot electroluminescence (EL) with a circular polarization | |
| degree up to 35% at zero applied magnetic field. The injection of spin | |
| polarized electrons is achieved by combining ultrathin CoFeB electrodes on top | |
| of a spin-LED device with p-type InGaAs quantum dots in the active region. We | |
| measure an Overhauser shift of several $\mu$eV at zero magnetic field for the | |
| positively charged exciton (trion X$^+$) EL emission, which changes sign as we | |
| reverse the injected electron spin orientation. This is a signature of dynamic | |
| polarization of the nuclear spins in the quantum dot induced by the hyperfine | |
| interaction with the electrically injected electron spin. This study paves the | |
| way for electrical control of nuclear spin polarization in a single quantum dot | |
| without any external magnetic field.",1803.04309v1 | |
| 2018-06-20,Current-induced modulation of interfacial Dzyaloshinskii-Moriya interaction,"The Dzyaloshinskii-Moriya (DM) interaction is an antisymmetric exchange | |
| interaction that is responsible for the emergence of chiral magnetism. The | |
| origin of the DM interaction, however, remains to be identified albeit the | |
| large number of studies reported on related effects. It has been recently | |
| suggested that the DM interaction is equivalent to an equilibrium spin current | |
| density originating from spin-orbit coupling, an effect referred to as the spin | |
| Doppler effect. The model predicts that the DM interaction can be controlled by | |
| spin current injected externally. Here we show that the DM exchange constant | |
| ($D$) in W/CoFeB based heterostructures can be modulated with external current | |
| passed along the film plane. At higher current, $D$ decreases with increasing | |
| current, which we infer is partly due to the adiabatic spin transfer torque. At | |
| lower current, $D$ increases linearly with current regardless of the polarity | |
| of current flow. The rate of increase in $D$ with the current density agrees | |
| with that predicted by the model based on the spin Doppler effect. These | |
| results imply that the DM interaction at the HM/FM interface partly originates | |
| from an equilibrium interface spin (polarized) current which can be modulated | |
| externally.",1806.07746v2 | |
| 2018-06-25,Two-terminal spin-orbit torque magnetoresistive random access memory,"Spin-transfer torque magnetoresistive random access memory (STT-MRAM) is an | |
| attractive alternative to current random access memory technologies due to its | |
| non-volatility, fast operation and high endurance. STT-MRAM does though have | |
| limitations including the stochastic nature of the STT-switching and a high | |
| critical switching current, which makes it unsuitable for ultrafast operation | |
| at nanosecond and sub-nanosecond regimes. Spin-orbit torque (SOT) switching, | |
| which relies on the torque generated by an in-plane current, has the potential | |
| to overcome these limitations. However, SOT-MRAM cells studied so far use a | |
| three-terminal structure in order to apply the in-plane current, which | |
| increases the size of the cells. Here we report a two-terminal SOT-MRAM cell | |
| based on a CoFeB/MgO magnetic tunnel junction pillar on an ultrathin and narrow | |
| Ta underlayer. In this device, an in-plane and out-of-plane current are | |
| simultaneously generated upon application of a voltage, and we demonstrate that | |
| the switching mechanism is dominated by SOT. We also compare our device to a | |
| STT-MRAM cell built with the same architecture and show that critical write | |
| current in the SOT-MRAM cell is reduced by more than 70%.",1806.09713v2 | |
| 2018-09-14,Femtosecond control of terahertz spin-charge conversion in ferromagnetic heterostructures,"Employing electron spin instead of charge to develop spintronic devices holds | |
| the merits of low-power consumption in information technologies. Meanwhile, the | |
| demand for increasing speed in spintronics beyond current CMOS technology has | |
| further triggered intensive researches for ultrafast control of spins even up | |
| to unprecedent terahertz regime. The femtosecond laser has been emerging as a | |
| potential technique to generate an ultrafast spin-current burst for | |
| magnetization manipulation. However, there is a great challenge to establish | |
| all-optical control and monitor of the femtosecond transient spin current. Deep | |
| insights into the physics and mechanism are extremely essential for the | |
| technique. Here, we demonstrate coherently nonthermal excitation of femtosecond | |
| spin-charge current conversion parallel to the magnetization in W/CoFeB/Pt | |
| heterostructures driven by linearly polarized femtosecond laser pulses. Through | |
| systematical investigation we observe the terahertz emission polarization | |
| depends on both the magnetization direction and structural asymmetry. We | |
| attribute this phenomenon of the terahertz generation parallel to the | |
| magnetization induced by linearly polarized femtosecond laser pulses probably | |
| to inverse spin-orbit torque effect. Our work not only is beneficial to the | |
| deep understanding of spin-charge conversion and spin transportation, but also | |
| helps develop novel on-chip terahertz opto-spintronic devices.",1809.05391v2 | |
| 2018-11-21,Strong Rashba-Edelstein Effect-Induced Spin-Orbit Torques in Monolayer Transition-Metal Dichalcogenide/Ferromagnet Bilayers,"The electronic and optoelectronic properties of two dimensional materials | |
| have been extensively explored in graphene and layered transition metal | |
| dichalcogenides (TMDs). Spintronics in these two-dimensional materials could | |
| provide novel opportunities for future electronics, for example, efficient | |
| generation of spin current, which should enable the efficient manipulation of | |
| magnetic elements. So far, the quantitative determination of charge current | |
| induced spin current and spin-orbit torques (SOTs) on the magnetic layer | |
| adjacent to two-dimensional materials is still lacking. Here, we report a large | |
| SOT generated by current-induced spin accumulation through the Rashba-Edelstein | |
| effect in the composites of monolayer TMD (MoS$_2$ or WSe$_2$)/CoFeB bilayer. | |
| The effective spin conductivity corresponding to the SOT turns out to be almost | |
| temperature-independent. Our results suggest that the charge-spin conversion in | |
| the chemical vapor deposition-grown large-scale monolayer TMDs could | |
| potentially lead to high energy efficiency for magnetization reversal and | |
| convenient device integration for future spintronics based on two-dimensional | |
| materials.",1811.08583v1 | |
| 2020-01-15,Nonreciprocal surface acoustic wave propagation via magneto-rotation coupling,"One of the most fundamental forms of magnon-phonon interaction is an | |
| intrinsic property of magnetic materials, the ""magnetoelastic coupling"". This | |
| particular form of interaction has been the basis for describing magnetic | |
| materials and their strain related applications, where strain induces changes | |
| of internal magnetic fields. Different from the magnetoelastic coupling, more | |
| than 40 years ago, it was proposed that surface acoustic waves may induce | |
| surface magnons via rotational motion of the lattice in anisotropic magnets. | |
| However, a signature of this magnon-phonon coupling mechanism, termed | |
| magneto-rotation coupling, has been elusive. Here, we report the first | |
| observation and theoretical framework of the magneto-rotation coupling in a | |
| perpendicularly anisotropic ultra-thin film Ta/CoFeB(1.6 nm)/MgO, which | |
| consequently induces nonreciprocal acoustic wave attenuation with a | |
| unprecedented ratio up to 100$\%$ rectification at the theoretically predicted | |
| optimized condition. Our work not only experimentally demonstrates a | |
| fundamentally new path for investigating magnon-phonon coupling, but also | |
| justify the feasibility of the magneto-rotation coupling based application.",2001.05135v3 | |
| 2020-01-15,Backward volume vs Damon-Eshbach: a travelling spin wave spectroscopy comparison,"We compare the characteristics of electrically transduced Damon-Eshbach | |
| (DESWs) and backward volume (BVSWs) configurations within the same, 30 nm | |
| thick, ferromagnetic, CoFeB waveguide. Sub-micron U-shaped antennas are used to | |
| deliver the necessary in-plane and out-of-plane RF fields. We measure the | |
| spin-wave transmission with respect to in-plane field orientation, frequency | |
| and propagation distance. Unlike DESW, BVSWs are reciprocally transduced and | |
| collected for either direction of propagation, but their ability to transport | |
| energy is lower than DESWs for two reasons. This arises first because BVSW are | |
| inductively transduced less efficiently than DESWs. Also, in the range of | |
| wavevectors (~5 rad. um-1) typically excited by our antennas, the group | |
| velocity of BVSWs stays lower than that of DESW, which leads to reduced | |
| propagation ability that impact transmission signals in an exponential manner. | |
| In contrast, the group velocity of DESWs is maximum at low fields and decreases | |
| continuously with the applied field. The essential features of the measured SW | |
| characteristics are well reciprocated by a simple, 1-D analytical model which | |
| can be used to assess the potential of each configuration.",2001.05221v2 | |
| 2021-07-20,Spin-wave dispersion measurement by variable-gap propagating spin-wave spectroscopy,"Magnonics is seen nowadays as a candidate technology for energy-efficient | |
| data processing in classical and quantum systems. Pronounced nonlinearity, | |
| anisotropy of dispersion relations and phase degree of freedom of spin waves | |
| require advanced methodology for probing spin waves at room as well as at mK | |
| temperatures. Yet, the use of the established optical techniques like Brillouin | |
| light scattering (BLS) or magneto optical Kerr effect (MOKE) at ultra-low | |
| temperatures is forbiddingly complicated. By contrast, microwave spectroscopy | |
| can be used at all temperatures but is usually lacking spatial and wavenumber | |
| resolution. Here, we develop a variable-gap propagating spin-wave spectroscopy | |
| (VG-PSWS) method for the deduction of the dispersion relation of spin waves in | |
| wide frequency and wavenumber range. The method is based on the phase-resolved | |
| analysis of the spin-wave transmission between two antennas with variable | |
| spacing, in conjunction with theoretical data treatment. We validate the method | |
| for the in-plane magnetized CoFeB and YIG thin films in $k\perp B$ and | |
| $k\parallel B$ geometries by deducing the full set of material and spin-wave | |
| parameters, including spin-wave dispersion, hybridization of the fundamental | |
| mode with the higher-order perpendicular standing spin-wave modes and surface | |
| spin pinning. The compatibility of microwaves with low temperatures makes this | |
| approach attractive for cryogenic magnonics at the nanoscale.",2107.09363v1 | |
| 2017-03-18,Spin Based Biosensor with Hard Axis Assist for Enhanced Sensitivity,"We demonstrate the influence of hard axis assist on an in-plane polarized | |
| nanomagnet layer to greatly enhance the sensitivity of a magnetic nano particle | |
| (MNP) based MTJ biosensor. The hard axis assist has been provided to the | |
| sensing layer in the forms of spin Hall Effect (SHE) induced spin injected | |
| torque and stress based effective magnetic field induced torque separately. | |
| Present work mainly focuses on the efficient and qualitative detection of a | |
| single magnetic bead with the aim of detecting a single bimolecular recognition | |
| event at an extremely low analyte concentration. Interfacial spin current | |
| arising from spin orbit metal is expected to impose a torque on the free layer | |
| along sensitive direction improving the signal strength by a factor of ~ 6.5 | |
| for a 100 nm bead at a height of 500 nm above the sensor surface. Furthermore, | |
| the potentiality of a multiferroic composite consisting of a piezoelectric | |
| layer coupled with magnetostrictive CoFeB based MTJ has been investigated in | |
| the Biosensing applications. An external stress voltage of 500 mV has been | |
| observed to be sufficient to enhance the sensitivity (~ 6 times). The use of | |
| nanoscaled spin devices and the absence of external magnetic field operated | |
| magnetization rotation facilitates in achieving highly compact and extremely | |
| low power designs. This establishes the possibility of utilizing the present | |
| schemes for advanced, highly sensitive, miniaturized and low power bioassaying | |
| system-on-chip applications. Numerical results were compared with some earlier | |
| reported experimental results to validate our proposed model.",1704.01555v1 | |
| 2017-04-20,Coupled mode theory for the acoustic wave and spin wave interaction in the magphonic crystals: Propagating magnetoelastic waves,"We have investigated co-directional and contra-directional couplings between | |
| spin wave and acoustic wave in one-dimensional periodic structure (magphonic | |
| crystal). The system consists of two ferromagnetic layers alternating in space. | |
| We have taken into consideration materials commonly used in magnonics: yttrium | |
| iron garnet, CoFeB, permalloy, and cobalt. The coupled mode theory (CMT) | |
| formalism have been successfully implemented to describe magnetoelastic | |
| interaction as a periodic perturbation in the magphonic crystal. The results of | |
| CMT calculations have been verified by more rigorous simulations by | |
| frequency-domain plane wave method and time-domain finite element method. The | |
| presented resonant coupling in the magphonic crystal is an active in-space | |
| mechanism which spatially transfers energy between propagating spin and | |
| acoustic modes, thus creating propagating magnetoelastic wave. We have shown, | |
| that CMT analysis of the magnetoelastic coupling is an useful tool to optimize | |
| and design a spin wave - acoustic wave transducer based on a magphonic | |
| crystals. The effect of spin wave damping has been included to the model to | |
| discuss the efficiency of such a device. Our model shows that it is possible to | |
| obtain forward conversion of the acoustic wave to the spin wave in case of | |
| co-directional coupling and backward conversion in case of contra-directional | |
| coupling.",1704.06118v1 | |
| 2018-07-17,Large anomalous Nernst effect in thin films of the Weyl semimetal Co2MnGa,"The magneto-thermoelectric properties of Heusler compound thin films are very | |
| diverse. Here, we discuss the anomalous Nernst response of Co$_2$MnGa thin | |
| films. We systematically study the anomalous Nernst coefficient as a function | |
| of temperature, and we show that unlike the anomalous Hall effect, the | |
| anomalous Nernst effect in Co$_2$MnGa strongly varies with temperature. We | |
| exploit the on-chip thermometry technique to quantify the thermal gradient, | |
| which enables us to directly evaluate the anomalous Nernst coefficient. We | |
| compare these results to a reference CoFeB thin film. We show that the | |
| 50-nm-thick Co$_2$MnGa films exhibit a large anomalous Nernst effect of | |
| -2$\mu$V/K at 300 K, whereas the 10-nm-thick Co$_2$MnGa film exhibits a | |
| significantly smaller anomalous Nernst coefficient despite having similar | |
| volume magnetizations. These findings suggest that the microscopic origin of | |
| the anomalous Nernst effect in Co$_2$MnGa is complex and may contain | |
| contributions from skew-scattering, side-jump or intrinsic Berry phase. In any | |
| case, the large anomalous Nernst coefficent of Co$_2$MnGa thin films at room | |
| temperature makes this material system a very promising candidate for efficient | |
| spin-caloritronic devices.",1807.06487v1 | |
| 2019-01-05,Demonstration of a strain-mediated magnetoelectric write and read unit in a Co60Fe20B20/ Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructure,"Taking advantage of the Magnetoelectric (ME) and its inverse effect, this | |
| article demonstrates strain-mediated magnetoelectric write and read operations | |
| simultaneously in Co60Fe20B20/ Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructures | |
| without using any symmetry breaking magnetic field at room temperature. By | |
| applying an external DC-voltage across a (011)-cut PMN-PT substrate, the | |
| ferroelectric polarization is re-oriented, which results in an anisotropic | |
| in-plane strain that transfers to the CoFeB thin film and changes its magnetic | |
| anisotropy Hk. The change in Hk in-turn results in a 90o rotation of the | |
| magnetic easy axis for sufficiently high voltages. Simultaneously, the inverse | |
| effect is employed to read changes of the magnetic properties. Because the | |
| Piezoelectric (PE)/FerroMagnetic (FM) system is fully coupled, the change of | |
| magnetization in FM induces an elastic stress in the PE layer, which generates | |
| a piezoelectric potential in the system that can be used to readout the | |
| magnetic state of the FM layer. Our experimental results are in excellent | |
| qualitative agreement with a recently proposed, experimentally benchmarked | |
| equivalent circuit model that considers how magnetic properties are | |
| electrically controlled in such ME/PE heterostructure and how a back-voltage is | |
| generated due to changing magnetic properties in a self-consistent model.",1901.01368v1 | |
| 2019-01-24,Topology-Dependent Brownian Gyromotion of a Single Skyrmion,"Non-interacting particles exhibiting Brownian motion have been observed in | |
| many occasions of sciences, such as molecules suspended in liquids, optically | |
| trapped microbeads, and spin textures in magnetic materials. In particular, a | |
| detailed examination of Brownian motion of spin textures is important for | |
| designing thermally stable spintronic devices which motivates the present | |
| study. In this Letter, through using temporally and spatially resolved polar | |
| magneto-optic Kerr effect (MOKE) microscopy, we have experimentally observed | |
| the thermal fluctuation-induced random walk of a single isolated N\'eel-type | |
| magnetic skyrmion in an interfacially asymmetric Ta/CoFeB/TaOx multilayer. An | |
| intriguing topology dependent Brownian gyromotion behavior of skyrmions has | |
| been identified. The onset of Brownian gyromotion of a single skyrmion induced | |
| by the thermal effects, including a nonlinear temperature-dependent diffusion | |
| coefficient and topology-dependent gyromotion are further formulated based on | |
| the stochastic Thiele equation. The experimental and numerical demonstration of | |
| topology-dependent Brownian gyromotion of skyrmions can be useful for | |
| understanding the nonequilibrium magnetization dynamics and implementing | |
| spintronic devices.",1901.08206v2 | |
| 2018-02-02,Spin wave emission by spin-orbit torque antennas,"We study the generation of propagating spin waves in Ta/CoFeB waveguides by | |
| spin-orbit torque antennas and compare them to conventional inductive antennas. | |
| The spin-orbit torque was generated by a transverse microwave current across | |
| the magnetic waveguide. The detected spin wave signals for an in-plane | |
| magnetization across the waveguide (Damon-Eshbach configuration) exhibited the | |
| expected phase rotation and amplitude decay upon propagation when the current | |
| spreading was taken into account. Wavevectors up to about 6 rad/$\mu$m could be | |
| excited by the spin-orbit torque antennas despite the current spreading, | |
| presumably due to the non-uniformity of the microwave current. The relative | |
| magnitude of generated anti-damping spin-Hall and Oersted fields was calculated | |
| within an analytic model and it was found that they contribute approximately | |
| equally to the total effective field generated by the spin-orbit torque | |
| antenna. Due to the ellipticity of the precession in the ultrathin waveguide | |
| and the different orientation of the anti-damping spin-Hall and Oersted fields, | |
| the torque was however still dominated by the Oersted field. The prospects for | |
| obtaining a pure spin-orbit torque response are discussed, as are the energy | |
| efficiency and the scaling properties of spin-orbit torque antennas.",1802.00861v2 | |
| 2019-02-10,Evidence of Pure Spin-Current Generated by Spin Pumping in Interface Localized States in Hybrid Metal-Silicon-Metal Vertical Structures,"Due to the difficulty to grow high quality semiconductors on ferromagnetic | |
| metals, the study of spin diffusion transport in Si was only limited to lateral | |
| geometry devices. In this work, by using ultra-high vacuum wafer-bonding | |
| technique, we have successfully fabricated metal semiconductor metal | |
| CoFeB/MgO/Si/Pt vertical structures. We hereby demonstrate pure spin-current | |
| injection and transport in the perpendicular current flow geometry over a | |
| distance larger than 2\mu m in n-type Si at room temperature. In those | |
| experiments, a pure propagating spin-current is generated via ferromagnetic | |
| resonance spin-pumping and converted into a measurable voltage by using the | |
| inverse spin-Hall effect occurring in the top Pt layer. A systematic study by | |
| varying both Si and MgO thicknesses reveals the important role played by the | |
| localized states at the MgO/Si interface for the spin-current generation. | |
| Proximity effects involving indirect exchange interactions between the | |
| ferromagnet and the MgO/Si interface states appears to be a prerequisite to | |
| establish the necessary out-of-equilibrium spin-population in Si under the | |
| spin-pumping action.",1902.03652v1 | |
| 2019-02-19,Generation and Hall effect of skyrmions enabled via using nonmagnetic point contacts,"To enable functional skyrmion based spintronic devices, the controllable | |
| generation and manipulation of skyrmions is essential. While the generation of | |
| skyrmions by using a magnetic geometrical constriction has already been | |
| demonstrated, this approach is difficult to combine with a subsequent | |
| controlled manipulation of skyrmions. The high efficiency of skyrmion | |
| generation from magnetic constrictions limits the useful current density, | |
| resulting in stochastic skyrmion motion, which may obscure topological | |
| phenomena such as the skyrmion Hall effect. In order to address this issue, we | |
| designed a nonmagnetic conducting Ti/Au point contact in devices made of | |
| Ta/CoFeB/TaOx trilayer films. By applying high voltage pulses, we | |
| experimentally demonstrated that skyrmions can be dynamically generated. | |
| Moreover, the accompanied spin topology dependent skyrmion dynamics, the | |
| skyrmion Hall effect is also experimentally observed in the same devices. The | |
| creation process has been numerically reproduced through micromagnetic | |
| simulations in which the important role of skyrmion-antiskyrmion pair | |
| generation is identified. The motion and Hall effect of the skyrmions, | |
| immediately after their creation is described using a modified Thiele equation | |
| after taking into account the contribution from spatially inhomogeneous | |
| spin-orbit torques and the Magnus force. The simultaneous generation and | |
| manipulation of skyrmions using a nonmagnetic point contact could provide a | |
| useful pathway for designing novel skyrmion based devices.",1902.06954v1 | |
| 2020-04-05,Spin wave based tunable switch between superconducting flux qubits,"Quantum computing hardware has received world-wide attention and made | |
| considerable progress recently. YIG thin film have spin wave (magnon) modes | |
| with low dissipation and reliable control for quantum information processing. | |
| However, the coherent coupling between a quantum device and YIG thin film has | |
| yet been demonstrated. Here, we propose a scheme to achieve strong coupling | |
| between superconducting flux qubits and magnon modes in YIG thin film. Unlike | |
| the direct $\sqrt{N}$ enhancement factor in coupling to the Kittel mode or | |
| other spin ensembles, with N the total number of spins, an additional spatial | |
| dependent phase factor needs to be considered when the qubits are magnetically | |
| coupled with the magnon modes of finite wavelength. To avoid undesirable | |
| cancelation of coupling caused by the symmetrical boundary condition, a CoFeB | |
| thin layer is added to one side of the YIG thin film to break the symmetry. Our | |
| numerical simulation demonstrates avoided crossing and coherent transfer of | |
| quantum information between the flux qubits and the standing spin waves in YIG | |
| thin films. We show that the YIG thin film can be used as a tunable switch | |
| between two flux qubits, which have modified shape with small direct inductive | |
| coupling between them. Our results manifest that it is possible to couple flux | |
| qubits while suppressing undesirable cross-talk.",2004.02156v1 | |
| 2020-08-14,Spin-injection and spin-relaxation in p-doped InGaAs/GaAs quantum-dot spin light emitting diode at zero magnetic field,"We report on efficient spin injection in p-doped InGaAs/GaAs quantum-dot (QD) | |
| spin light emitting diode (spin-LED) under zero applied magnetic field. A high | |
| degree of electroluminescence circular polarization (Pc) ~19% is measured in | |
| remanence up to 100K. This result is obtained thanks to the combination of a | |
| perpendicularly magnetized CoFeB/MgO spin injector allowing efficient spin | |
| injection and an appropriate p-doped InGaAs/GaAs QD layer in the active region. | |
| By analyzing the bias and temperature dependence of the electroluminescence | |
| circular polarization, we have evidenced a two-step spin relaxation process. | |
| The first step occurs when electrons tunnel through the MgO barrier and travel | |
| across the GaAs depletion layer. The spin relaxation is dominated by the | |
| Dyakonov-Perel mechanism related to the kinetic energy of electrons, which is | |
| characterized by a bias dependent Pc. The second step occurs when electrons are | |
| captured into QDs prior to their radiative recombination with holes. The | |
| temperature dependence of Pc reflects the temperature induced modification of | |
| the QDs doping, together with the variation of the ratio between the charge | |
| carrier lifetime and the spin relaxation time inside the QDs. The understanding | |
| of these spin relaxation mechanisms is essential to improve the performance of | |
| spin LED for future spin optoelectronic applications at room temperature under | |
| zero applied magnetic field.",2008.06407v1 | |
| 2020-08-17,Enhancement of spin Hall conductivity in W-Ta alloy,"Generating pure spin currents via the spin Hall effect in heavy metals has | |
| been an active topic of research in the last decade. In order to reduce the | |
| energy required to efficiently switch neighbouring ferromagnetic layers for | |
| applications, one should not only increase the charge- to-spin conversion | |
| efficiency but also decrease the longitudinal resistivity of the heavy metal. | |
| In this work, we investigate the spin Hall conductivity in W_{1-x}Ta_{x} / | |
| CoFeB / MgO (x = 0 - 0.2) using spin torque ferromagnetic resonance | |
| measurements. Alloying W with Ta leads to a factor of two change in both the | |
| damping-like effective spin Hall angle (from - 0.15 to - 0.3) and longitudinal | |
| resistivity (60 - 120 {\mu}W cm). At 11% Ta concentration, a remarkably high | |
| spin Hall angle value of - 0.3 is achieved with a low longitudinal resistivity | |
| 100 {\mu}W cm, which could lead to a very low power consumption for this | |
| W-based alloy. This work demonstrates sputter-deposited W-Ta alloys could be a | |
| promising material for power-efficient spin current generation.",2008.07572v1 | |
| 2016-02-08,External-Field-Free Spin Hall Switching of Perpendicular Magnetic Nanopillar with a Dipole-Coupled Composite Structure,"Spin Hall effect (SHE) induced reversal of perpendicular magnetization has | |
| attracted significant interest, due to its potential to lead to low power | |
| memory and logic devices. However, the switching requires an assisted in-plane | |
| magnetic field, which hampers its practical applications. Here, we introduce a | |
| novel approach for external-field-free spin Hall switching of a perpendicular | |
| nanomagnet by utilizing a local dipolar field arising from an adjacent in-plane | |
| magnetic layer. Robust switching of perpendicular CoFeB nanopillars in a | |
| dipole-coupled composite stack is experimentally demonstrated in the absence of | |
| any external magnetic field, in consistent with the results of micromagnetic | |
| simulation. Large in-plane compensation field of about 135 Oe and out-of-plane | |
| loop shift of about 45 Oe / 10 7 A cm-2 are obtained in the nanopillar devices | |
| with composite structure. By performing micromagnetic simulations, we confirm | |
| the composite external-field-free switching strategy can also work for a 10 x | |
| 10 nm2 circular pillar. Compared with other proposed methods for | |
| external-field-free spin Hall switching of perpendicular magnetization, the | |
| dipole-coupled composite structure is compatible with a wide range of spin Hall | |
| systems and perpendicular magnetic tunnel junctions, paving the way towards | |
| practical SHE-based MRAM and logic applications.",1603.09624v2 | |
| 2017-02-16,Pumping laser excited spins through MgO barriers,"We present a study of the tunnel magneto-Seebeck (TMS) effect in MgO based | |
| magnetic tunnel junctions (MTJs). The electrodes consist of CoFeB with in-plane | |
| magnetic anisotropy. The temperature gradients which generate a voltage across | |
| the MTJs layer stack are created using laser heating. Using this method, the | |
| temperature can be controlled on the micrometer length scale: here, we | |
| investigate, how both, the TMS voltage and the TMS effect, depend on the size, | |
| position and intensity of the applied laser spot. For this study, a large | |
| variety of different temperature distributions was created across the junction. | |
| We recorded two-dimensional maps of voltages generated by heating in dependence | |
| of the laser spot position and the corresponding calculated TMS values. The | |
| voltages change in value and sign, from large positive values when heating the | |
| MTJ directly in the centre to small values when heating the junction on the | |
| edges and even small negative values when heating the sample away from the | |
| junction. Those zero crossings lead to very high calculated TMS ratios. Our | |
| systematic analysis shows, that the distribution of the temperature gradient is | |
| essential, to achieve high voltage signals and reasonable resulting TMS ratios. | |
| Furthermore, artefacts on the edges produce misleading results, but also open | |
| up further possibilities of more complex heating scenarios for | |
| spincaloritronics in spintronic devices.",1702.05038v1 | |
| 2017-02-21,All-optical Detection of Spin Hall Angle in W/CoFeB/SiO2 Heterostructures by Varying Tungsten Layer Thickness,"The development of advanced spintronics devices hinges on the efficient | |
| generation and utilization of pure spin current. In materials with large | |
| spin-orbit coupling, the spin Hall effect may convert charge current to pure | |
| spin current and a large conversion efficiency, which is quantified by spin | |
| Hall angle (SHA), is desirable for the realization of miniaturized and energy | |
| efficient spintronic devices. Here, we report a giant SHA in beta-tungsten | |
| (\b{eta}-W) thin films in Sub/W(t)/Co20Fe60B20(3 nm)/SiO2(2 nm) | |
| heterostructures with variable W thickness. We employed an all-optical | |
| time-resolved magneto-optical Kerr effect microscope for an unambiguous | |
| determination of SHA using the principle of modulation of Gilbert damping of | |
| the adjacent ferromagnetic layer by the spin-orbit torque from the W layer. A | |
| non-monotonic variation of SHA with W layer thickness (t) is observed with a | |
| maximum of about 0.4 at about t = 3 nm, followed by a sudden reduction to a | |
| very low value at t = 6 nm. This variation of SHA with W-thickness correlates | |
| well with the thickness dependent structural phase transition and resistivity | |
| variation of W above the spin diffusion length of W, while below this length | |
| the interfacial electronic effect at W/CoFeB influences the estimation of SHA.",1702.06258v1 | |
| 2019-05-27,Unidirectional planar Hall voltages induced by surface acoustic waves in ferromagnetic thin films,"The electromotive forces induced by surface acoustic waves (SAWs) are | |
| investigated in ferromagnetic thin films. CoFeB thin films deposited on | |
| LiNbO$_3$ substrates are patterned into Hall-bars to study the acoustoelectric | |
| transport properties of the device. The longitudinal and transverse dc voltages | |
| that develop in the Hall bars, which are parallel and orthogonal to the flow of | |
| the SAW, respectively, are measured under application of an in-plane magnetic | |
| field. The longitudinal voltage scales linearly with the SAW power and reverses | |
| its polarity upon changing the direction to which the SAW propagates, | |
| suggesting generation of a dc acoustic current via the SAW excitation. The | |
| magnetic field has little influence on the acoustic current. In contrast, the | |
| SAW induced transverse voltage shows significant dependence on the relative | |
| angle between the magnetic field and the SAW propagation direction. Such field | |
| angle dependent voltage resembles that of the planar Hall voltage induced by | |
| electric current. Interestingly, the angle dependent acoustic transverse | |
| voltage does not depend on the SAW propagation direction. Moreover, the | |
| magnitude of the equivalent angle dependent acoustic transverse resistance is | |
| more than one order of magnitude larger than that of the planar Hall | |
| resistance. These results show the unique acoustoelectric transport properties | |
| of ferromagnetic thin films.",1905.11224v1 | |
| 2020-07-23,Electrical Detection of Light Helicity using a Quantum Dots based Hybrid Device at Zero Magnetic Field,"Photon helicity-dependent photocurrent is measured at zero magnetic field on | |
| a device based on an ensemble of InGaAs/GaAs quantum dots that are embedded | |
| into a GaAs-based p-i-n diode. Our main goal is to take advantage of the long | |
| electron spin relaxation time expected in these nano-objects. In these | |
| experiments, no external magnetic field is required thanks to the use of an | |
| ultrathin magnetic CoFeB/MgO electrode, presenting perpendicular magnetic | |
| anisotropy (PMA). We observe a clear asymmetry of the photocurrent measured | |
| under respective right and left polarized light that follows the hysteresis of | |
| the magnetic layer. The amplitude of this asymmetry at zero magnetic field | |
| decreases with increasing temperatures and can be controlled with the bias. | |
| Polarization-resolved photoluminescence is detected in parallel while the | |
| device is operated as a photodetector. This demonstrates the multifunctional | |
| capabilities of the device and gives valuable insights into the spin relaxation | |
| of the electrons in the quantum dots.",2007.12054v1 | |
| 2020-12-02,Engineered magnetization and exchange stiffness in direct-write Co-Fe nanoelements,"Media with engineered magnetization are essential building blocks in | |
| superconductivity, magnetism and magnon spintronics. However, the established | |
| thin-film and lithographic techniques insufficiently suit the realization of | |
| planar components with on-demand-tailored magnetization in the lateral | |
| dimension. Here, we demonstrate the engineering of the magnetic properties of | |
| CoFe-based nanodisks fabricated by the mask-less technique of focused electron | |
| beam induced deposition (FEBID). The material composition in the nanodisks is | |
| tuned \emph{in-situ} via the e-beam waiting time in the FEBID process and their | |
| post-growth irradiation with Ga ions. The magnetization $M_s$ and exchange | |
| stiffness $A$ of the disks are deduced from perpendicular ferromagnetic | |
| resonance measurements. The achieved $M_s$ variation in the broad range from | |
| $720$ emu/cm$^3$ to $1430$ emu/cm$^3$ continuously bridges the gap between the | |
| $M_s$ values of such widely used magnonic materials as permalloy and CoFeB. The | |
| presented approach paves a way towards nanoscale 2D and 3D systems with | |
| controllable and space-varied magnetic properties.",2012.01481v1 | |
| 2021-04-05,"Analyser-free, intensity-based wide-field magneto-optical microscopy","In conventional Kerr- and Faraday microscopy the sample is illuminated with | |
| plane-polarised light and a magnetic domain contrast is generated by an | |
| analyser making use of the Kerr- or Faraday rotation. In this paper we | |
| demonstrate possibilities of analyser-free magneto-optical microscopy based on | |
| magnetisation-dependent intensity modulations of the light: (i) The transverse | |
| Kerr effect can be applied for in-plane magnetised material, demonstrated for | |
| an FeSi sheet. (ii) Illuminating the same sample with circularly polarised | |
| light leads to a domain contrast with a different symmetry as the conventional | |
| Kerr contrast. (iii) Circular polarisation can also be used for perpendicularly | |
| magnetised material, demonstrated for a garnet film and an ultrathin CoFeB | |
| film. (iv) Plane-polarised light at a specific angle can be employed for both, | |
| in-plane and perpendicular media. (v) Perpendicular light incidence leads to a | |
| domain contrast on in-plane materials that is quadratic in the magnetisation | |
| and to a domain boundary contrast. (vi) Domain contrast can even be obtained | |
| without polariser. In cases (ii) and (iii), the contrast is generated by MCD | |
| (Magnetic Circular Dichroism), while MLD (Magnetic Linear Dichroism) is | |
| responsible for the contrast in case (v). The domain boundary contrast is due | |
| to the magneto-optical gradient effect in metallic samples. A domain boundary | |
| contrast can also arise due to interference of phase-shifted magneto-optical | |
| amplitudes. An explanation of these contrast phenomena is provided in terms of | |
| Maxwell-Fresnel theory.",2104.01831v2 | |
| 2021-06-29,Spin Hall effect in a spin-1 chiral semimetal,"Spin-1 chiral semimetal is a new state of quantum matter hosting | |
| unconventional chiral fermions that extend beyond the common Dirac and Weyl | |
| fermions. B20-type CoSi is a prototypal material that accommodates such an | |
| exotic quasiparticle. To date, the spin transport properties in the spin-1 | |
| chiral semimetals, have not been explored yet. In this work, we fabricated | |
| B20-CoSi thin films on sapphire c-plane substrates by magnetron sputtering and | |
| studied the spin Hall effect (SHE) by combining experiments and | |
| first-principles calculations. The SHE of CoSi using CoSi/CoFeB/MgO | |
| heterostructures was investigated via spin Hall magnetoresistance and harmonic | |
| Hall measurements. First-principles calculations yield an intrinsic spin Hall | |
| conductivity (SHC) at the Fermi level that is consistent with the experiments | |
| and reveal its unique Fermi-energy dependence. Unlike the Dirac and Weyl | |
| fermion-mediated Hall conductivities that exhibit a peak-like structure | |
| centering around the topological node, SHC of B20-CoSi is odd and crosses zero | |
| at the node with two antisymmetric local extrema of opposite sign situated | |
| below and above in energy. Hybridization between Co d-Si p orbitals and | |
| spin-orbit coupling are essential for the SHC, despite the small (~1%) weight | |
| of Si p-orbital near the Fermi level. This work expands the horizon of | |
| topological spintronics and highlights the importance of Fermi-level tuning in | |
| order to fully exploit the topology of spin-1 chiral fermions for spin current | |
| generation.",2106.15107v1 | |
| 2021-11-13,360° polarization control of terahertz spintronic emitters using uniaxial FeCo/TbCo2/FeCo trilayers,"Polarization control of THz light is of paramount interest for the numerous | |
| applications offered in this frequency range. Recent developments in THz | |
| spintronic emitters allow for a very efficient broadband emission, and | |
| especially unique is their ability of THz polarization switching through | |
| magnetization control of the ferromagnetic layer. Here we present an improved | |
| scheme to achieve full 360{\deg} nearly coherent polarization rotation that | |
| does not require multipolar or rotating external magnetic bias nor complex | |
| cascaded emitters. By replacing the FM layer of the spintronic emitter with a | |
| carefully designed FeCo/TbCo2/FeCo anisotropic heterostructure, we | |
| experimentally demonstrate Stoner-Wohlfarth-like coherent rotation of the THz | |
| polarization over a full 2pi azimuth only by a bipolar variation of the | |
| strength of the hard axis field, and with only a negligible decrease in the | |
| emission efficiency as compared to standard Pt/CoFeB/W inverse spin Hall | |
| emitters. THz measurements are in agreement with our model of the non-perfect | |
| Stoner-Wohlfarth behaviour. These emitters are well adapted for the | |
| implementation of polarimetric characterization not requiring any mechanically | |
| rotating polarizing elements. An example is given with the characterization of | |
| the birefringence in a quartz plate.",2111.07118v1 | |
| 2022-06-07,Non-volatile electric control of spin-orbit torques in an oxide two-dimensional electron gas,"Spin-orbit torques (SOTs) have opened a novel way to manipulate the | |
| magnetization using in-plane current, with a great potential for the | |
| development of fast and low power information technologies. It has been | |
| recently shown that two-dimensional electron gases (2DEGs) appearing at oxide | |
| interfaces provide a highly efficient spin-to-charge current interconversion. | |
| The ability to manipulate 2DEGs using gate voltages could offer a degree of | |
| freedom lacking in the classical ferromagnetic/spin Hall effect bilayers for | |
| spin-orbitronics, in which the sign and amplitude of SOTs at a given current | |
| are fixed by the stack structure. Here, we report the non-volatile | |
| electric-field control of SOTs in an oxide-based Rashba-Edelstein 2DEG. We | |
| demonstrate that the 2DEG is controlled using a back-gate electric-field, | |
| providing two remanent and switchable states, with a large resistance contrast | |
| of 1064%. The SOTs can then be controlled electrically in a non-volatile way, | |
| both in amplitude and in sign. This achievement in a 2DEG-CoFeB/MgO | |
| heterostructures with large perpendicular magnetization further validates the | |
| compatibility of oxide 2DEGs for magnetic tunnel junction integration, paving | |
| the way to the advent of electrically reconfigurable SOT MRAMS circuits, SOT | |
| oscillators, skyrmion and domain-wall-based devices, and magnonic circuits.",2206.03068v1 | |
| 2022-08-09,Growth-dependent Interlayer Chiral Exchange and Field-free Switching,"Interfacial Dzyaloshinskii-Moriya interaction (DMI) has long been observed in | |
| normal metal/ferromagnetic multilayers, enabling the formation of chiral domain | |
| walls, skyrmions and other 2D antisymmetric spin textures confined within a | |
| single ferromagnetic layer, while more recent works on interlayer DMI reveal | |
| new pathways in realizing novel chiral 3D spin textures between two separate | |
| layers.Here, we report on interlayer DMI between two orthogonally magnetized | |
| ferromagnetic layers (CoFeB/Co) mediated by a Pt layer, and confirm the chiral | |
| nature of the observed effective field of up to 37 Oe through asymmetric | |
| hysteresis loops under in-plane field.We highlight the importance of | |
| growth-induced in-plane symmetry breaking, resulting in a sizable interlayer | |
| DMI and a universal characteristic vector through wedge deposition of the | |
| samples.We further perform deterministic current-driven magnetization switching | |
| in the perpendicularly magnetized Co layer utilizing solely the effective field | |
| from the interlayer DMI.These results demonstrate the potential of interlayer | |
| DMI in facilitating deterministic field-free switching in spin memory | |
| applications.",2208.04492v1 | |
| 2022-10-12,Depth-dependent magnetic crossover in a room-temperature skyrmion-hosting multilayer,"Skyrmion-hosting multilayer stacks are promising avenues for applications, | |
| although little is known about the depth dependence of the magnetism. We | |
| address this by reporting the results of circular dichroic resonant elastic | |
| x-ray scattering (CD-REXS), micromagnetic simulations, and low-energy muon-spin | |
| rotation (LE-$\mu^+$SR) measurements on a stack comprising | |
| [Ta/CoFeB/MgO]$_{16}$/Ta on a Si substrate. Energy-dependent CD-REXS shows a | |
| continuous, monotonic evolution of the domain-wall helicity angle with incident | |
| energy, consistent with a three-dimensional hybrid domain-wall-like structure | |
| that changes from N\'eel-like near the surface to Bloch-like deeper within the | |
| sample. LE-$\mu^+$SR reveals that the magnetic field distribution in the | |
| trilayers near the surface of the stack is distinct from that in trilayers | |
| deeper within the sample. Our micromagnetic simulations support a quantitative | |
| analysis of the $\mu^+$SR results. By increasing the applied magnetic field, we | |
| find a reduction in the volume occupied by domain walls at all depths, | |
| consistent with a crossover into a region dominated by skyrmions above | |
| approximately 180 mT.",2210.06070v2 | |
| 2022-12-15,Emulation of Neuron and Synaptic Functions in Spin-Orbit Torque Domain Wall Devices,"Neuromorphic computing (NC) architecture has shown its suitability for | |
| energy-efficient computation. Amongst several systems, spin-orbit torque (SOT) | |
| based domain wall (DW) devices are one of the most energy-efficient contenders | |
| for NC. To realize spin-based NC architecture, the computing elements such as | |
| synthetic neurons and synapses need to be developed. However, there are very | |
| few experimental investigations on DW neurons and synapses. The present study | |
| demonstrates the energy-efficient operations of neurons and synapses by using | |
| novel reading and writing strategies. We have used a W/CoFeB-based | |
| energy-efficient SOT mechanism to drive the DWs at low current densities. We | |
| have used the concept of meander devices for achieving synaptic functions. By | |
| doing this, we have achieved 9 different resistive states in experiments. We | |
| have experimentally demonstrated the functional spike and step neurons. | |
| Additionally, we have engineered the anomalous Hall bars by incorporating | |
| several pairs, in comparison to conventional Hall crosses, to increase the | |
| sensitivity as well as signal-to-noise ratio (SNR). We performed micromagnetic | |
| simulations and transport measurements to demonstrate the above-mentioned | |
| functionalities.",2212.07833v1 | |
| 2023-01-10,Robust mutual synchronization in long spin Hall nano-oscillator chains,"Mutual synchronization of N serially connected spintronic nano-oscillators | |
| increases their coherence by a factor $N$ and their output power by $N^2$. | |
| Increasing the number of mutually synchronized nano-oscillators in chains is | |
| hence of great importance for better signal quality and also for emerging | |
| applications such as oscillator-based neuromorphic computing and Ising machines | |
| where larger N can tackle larger problems. Here we fabricate spin Hall | |
| nano-oscillator chains of up to 50 serially connected nano-constrictions in | |
| W/NiFe, W/CoFeB/MgO, and NiFe/Pt stacks and demonstrate robust and complete | |
| mutual synchronization of up to 21 nano-constrictions, reaching linewidths of | |
| below 200 kHz and quality factors beyond 79,000, while operating at 10 GHz. We | |
| also find a square increase in the peak power with the increasing number of | |
| mutually synchronized oscillators, resulting in a factor of 400 higher peak | |
| power in long chains compared to individual nano-constrictions. Although chains | |
| longer than 21 nano-constrictions also show complete mutual synchronization, it | |
| is not as robust and their signal quality does not improve as much as they | |
| prefer to break up into partially synchronized states. The low current and low | |
| field operation of these oscillators along with their wide frequency tunability | |
| (2-28 GHz) with both current and magnetic fields, make them ideal candidates | |
| for on-chip GHz-range applications and neuromorphic computing.",2301.03859v1 | |
| 2023-02-02,Controlling the Skyrmion Density and Size for Quantized Convolutional Neural Networks,"Skyrmion devices show energy efficient and high integration data storage and | |
| computing capabilities. Herein, we present the results of experimental and | |
| micromagnetic investigations of the creation and stability of magnetic | |
| skyrmions in the Ta/IrMn/CoFeB/MgO thin film system. We investigate the | |
| magnetic-field dependence of the skyrmion density and size using polar magneto | |
| optical Kerr effect MOKE microscopy supported by a micromagnetic study. The | |
| evolution of the topological charge with time under a magnetic field is | |
| investigated, and the transformation dynamics are explained. Furthermore, | |
| considering the voltage control of these skyrmion devices, we evaluate the | |
| dependence of the skyrmion size and density on the Dzyaloshinskii Moriya | |
| interaction and the magnetic anisotropy. We furthermore propose a skyrmion | |
| based synaptic device based on the results of the MOKE and micromagnetic | |
| investigations. We demonstrate the spin-orbit torque controlled discrete | |
| topological resistance states with high linearity and uniformity in the device. | |
| The discrete nature of the topological resistance makes it a good candidate to | |
| realize hardware implementation of weight quantization in a quantized neural | |
| network (QNN). The neural network is trained and tested on the CIFAR10 dataset, | |
| where the devices act as synapses to achieve a recognition accuracy of 87%, | |
| which is comparable to the result of ideal software-based methods.",2302.01390v1 | |
| 2023-04-16,Anomalous and Topological Hall Resistivity in Ta/CoFeB/MgO Magnetic Systems for Neuromorphic Computing Applications,"Topologically protected spin textures, such as magnetic skyrmions, have the | |
| potential for dense data storage as well as energy-efficient computing due to | |
| their small size and a low driving current. The evaluation of the writing and | |
| reading of the skyrmion's magnetic and electrical characteristics is a key step | |
| toward the implementation of these devices. In this paper, we present the | |
| magnetic heterostructure Hall bar device and study the anomalous Hall and | |
| topological Hall signals in the device. Using the combination of different | |
| measurements like magnetometry at different temperatures, Hall effect | |
| measurement from 2K to 300K, and magnetic force microscopy imaging, we | |
| investigate the magnetic and electrical characteristics of the magnetic | |
| structure. We measure the skyrmion topological resistivity at different | |
| temperatures as a function of the magnetic field. The topological resistivity | |
| is maximum around the zero magnetic field and it decreases to zero at the | |
| saturating field. This is further supported by MFM imaging. Interestingly the | |
| resistivity decreases linearly with the field, matching the behavior observed | |
| in the corresponding micromagnetic simulations. We combine the experimental | |
| results with micromagnetic simulations, thus propose a skyrmion-based synaptic | |
| device and show spin-orbit torque-controlled potentiation/depression in the | |
| device. The device performance as the synapse for neuromorphic computing is | |
| further evaluated in a convolutional neural network CNN. The neural network is | |
| trained and tested on the MNIST data set we show devices acting as synapses | |
| achieving a recognition accuracy close to 90%, on par with the ideal | |
| software-based weights which offer an accuracy of 92%.",2304.07742v1 | |
| 2023-06-28,Suppression of the spin waves nonreciprocity due to interfacial Dzyaloshinskii Moriya interaction by lateral confinement in magnetic nanostructures,"Despite the huge recent interest towards chiral magnetism related to the | |
| interfacial Dzyaloshinskii Moriya interaction (iDMI) in layered systems, there | |
| is a lack of experimental data on the effect of iDMI on the spin waves | |
| eigenmodes of laterally confined nanostructures. Here we exploit Brillouin | |
| Light Scattering (BLS) to analyze the spin wave eigenmodes of non-interacting | |
| circular and elliptical dots, as well as of long stripes, patterned starting | |
| from a Pt(3.4 nm)/CoFeB(0.8 nm) bilayer, with lateral dimensions ranging from | |
| 100 nm to 400 nm. Our experimental results, corroborated by micromagnetic | |
| simulations based on the GPU-accelerated MuMax3 software package, provide | |
| evidence for a strong suppression of the frequency asymmetry between | |
| counter-propagating spin waves (corresponding to either Stokes or anti-Stokes | |
| peaks in BLS spectra), when the lateral confinement is reduced from 400 nm to | |
| 100 nm, i.e. when it becomes lower than the light wavelength. Such an evolution | |
| reflects the modification of the spin wave character from propagating to | |
| stationary and indicates that the BLS based method of quantifying the i-DMI | |
| strength from the frequency difference of counter propagating spin waves is not | |
| applicable in the case of magnetic elements with lateral dimension below about | |
| 400 nm.",2306.16310v1 | |
| 2023-09-27,Impact of surface anisotropy on the spin-wave dynamics in thin ferromagnetic film,"The spin-wave dynamics in the thin CoFeB film in Damon-Eshbach geometry are | |
| studied in three cases of boundary conditions -- free boundary conditions, | |
| symmetrical surface anisotropy, and one-sided surface anisotropy. The | |
| analytical model created by Wolfram and De Wames was extended to include | |
| perpendicular surface anisotropy in boundary conditions. Its comparison with | |
| numerical simulations demonstrate perfect agreement between the approaches. The | |
| analysis of the dispersion relation indicates that the presence of surface | |
| anisotropy increases the avoided crossing size between Damon-Eshbach mode and | |
| perpendicular standing modes. Additionally, asymmetrical one-sided surface | |
| anisotropy induces nonreciprocity in the dispersion relation. In-depth analysis | |
| of the avoided crossing size is conducted for systems with different boundary | |
| conditions, different thicknesses, surface anisotropy constant values, and | |
| external magnetic fields. It shows the significant role of the strength of | |
| surface localization of Damon-Eshbach mode and the symmetry of perpendicular | |
| standing modes in the avoided crossing broadening. Interestingly, for specific | |
| set of parameters the interaction between the particular modes can be | |
| suppressed, resulting in a mode crossing. Such a crossing, which occurs only on | |
| one side of the dispersion relation in a one-sided surface anisotropy system, | |
| can be utilized in nonreciprocal devices.",2309.15583v1 | |
| 2023-11-15,Low voltage local strain enhanced switching of magnetic tunnel junctions,"Strain-controlled modulation of the magnetic switching behavior in magnetic | |
| tunnel junctions (MTJs) could provide the energy efficiency needed to | |
| accelerate the use of MTJs in memory, logic, and neuromorphic computing, as | |
| well as an additional way to tune MTJ properties for these applications. | |
| State-of-the-art CoFeB-MgO based MTJs still require too high voltages to alter | |
| their magnetic switching behavior with strain. In this study, we demonstrate | |
| strain-enhanced field switching of nanoscale MTJs through electric field | |
| control via voltage applied across local gates. The results show that | |
| record-low voltage down to 200 mV can be used to control the switching field of | |
| the MTJ through enhancing the magnetic anisotropy, and that tunnel | |
| magnetoresistance is linearly enhanced with voltage through straining the | |
| crystal structure of the tunnel barrier. These findings underscore the | |
| potential of electric field manipulation and strain engineering as effective | |
| strategies for tailoring the properties and functionality of nanoscale MTJs.",2311.08984v2 | |
| 2023-11-24,Even-in-magnetic-field part of transverse resistivity as a probe of magnetic order,"The detection of a voltage transverse to both an applied current and a | |
| magnetic field is one of the most common characterization techniques in | |
| solid-state physics. The corresponding component of the resistivity tensor | |
| $\rho_{ij}$ can be separated into odd and even parts with respect to the | |
| applied magnetic field. The former contains information, for example, about the | |
| ordinary or anomalous Hall effect. The latter is typically ascribed to | |
| experimental artefacts and ignored. We here show that upon suppressing these | |
| artefacts in carefully controlled experiments, useful information remains. We | |
| first investigate the well-explored ferromagnet CoFeB, where the even part of | |
| $\rho_{yx}$ contains a contribution from the anisotropic magnetoresistance, | |
| which we confirm by Stoner-Wohlfarth modelling. We then apply our approach to | |
| magnetotransport measurements in $\rm Mn_5Si_3$ thin films with a complex | |
| compensated magnetic order. In this material, the even part of the transverse | |
| signal is sizable only in the low-spin-symmetry phase below $\approx 80$ K and | |
| thus offers a simple and readily available probe of the magnetic order.",2311.14498v1 | |
| 2024-03-25,Skyrmionic device for three dimensional magnetic field sensing enabled by spin-orbit torques,"Magnetic skyrmions are topologically protected local magnetic solitons that | |
| are promising for storage, logic or general computing applications. In this | |
| work, we demonstrate that we can use a skyrmion device based on [W/CoFeB/MgO] 1 | |
| 0 multilayers for three-dimensional magnetic field sensing enabled by | |
| spin-orbit torques (SOT). We stabilize isolated chiral skyrmions and stripe | |
| domains in the multilayers, as shown by magnetic force microscopy images and | |
| micromagnetic simulations. We perform magnetic transport measurements to show | |
| that we can sense both in-plane and out-of-plane magnetic fields by means of a | |
| differential measurement scheme in which the symmetry of the SOT leads to | |
| cancelation of the DC offset. With the magnetic parameters obtained by | |
| vibrating sample magnetometry and ferromagnetic resonance measurements, we | |
| perform finite-temperature micromagnetic simulations, where we investigate the | |
| fundamental origin of the sensing signal. We identify the topological | |
| transformation between skyrmions, stripes and type-II bubbles that leads to a | |
| change in the resistance that is read-out by the anomalous Hall effect. Our | |
| study presents a novel application for skyrmions, where a differential | |
| measurement sensing concept is applied to quantify external magnetic fields | |
| paving the way towards more energy efficient applications in skyrmionics based | |
| spintronics.",2403.16725v1 | |
| 2020-09-14,Large field-like torque in amorphous Ru2Sn3 originated from the intrinsic spin Hall effect,"We investigated temperature dependent current driven spin-orbit torques in | |
| magnetron sputtered Ru2Sn3 (4 and 10 nm) /Co20Fe60B20 (5 nm) layered structures | |
| with in-plane magnetic anisotropy. The room temperature damping-like and | |
| field-like spin torque efficiencies of the amorphous Ru2Sn3 films were measured | |
| to be 0.14 +- 0.008 (0.07 +- 0.012) and -0.03 +- 0.006 (-0.20 +- 0.009), for | |
| the 4 (10 nm) films respectively, by utilizing the second harmonic Hall | |
| technique. The large field-like torque in the relatively thicker Ru2Sn3 (10 nm) | |
| thin film is unique compared to the traditional spin Hall materials interfaced | |
| with thick magnetic layers with in-plane magnetic anisotropy which typically | |
| have dominant damping-like and negligible field-like torques. Additionally, the | |
| observed room temperature field-like torque efficiency in Ru2Sn3 (10 nm)/CoFeB | |
| (5 nm) is up to three times larger than the damping-like torque (-0.20 +- 0.009 | |
| and 0.07 +- 0.012, respectively) and thirty times larger at 50 K (-0.29 +- | |
| 0.014 and 0.009 +- 0.017, respectively). The temperature dependence of the | |
| field-like torques show dominant contributions from the intrinsic spin Hall | |
| effect while the damping-like torques show dominate contributions from the | |
| extrinsic spin Hall effects, skew scattering and side jump. Through macro-spin | |
| calculations, we found that including field-like torques on the order or larger | |
| than the damping-like torque can reduce the switching critical current and | |
| decrease magnetization procession for a perpendicular ferromagnetic layer.",2009.06711v2 | |
| 2021-11-09,Spintronic emitters for super-resolution in THz-spectral imaging,"THz-spectroscopy is an attractive imaging tool for scientific research, | |
| especially in life science, offering non-destructive interaction with matter | |
| due to its low photon energies. However, wavelengths above $100{\mu}m$ | |
| principally limit its spatial resolution in the far-field by diffraction to | |
| this regime, making it not sufficient to image biological cells in the | |
| micrometer scale. Therefore, super-resolution imaging techniques are required | |
| to overcome this restriction. Near-field-imaging using spintronic emitters | |
| offers the most feasible approach because of its simplicity and potential for | |
| wide-ranging applications. In our study, we investigate THz-radiation generated | |
| by fs-laser-pulses in CoFeB/Pt heterostructures, based on spin currents, | |
| detected by commercial LT-GaAs Auston switches. The spatial resolution is | |
| evaluated applying a 2D scanning technique with motorized stages allowing | |
| scanning steps in the sub-micrometer range. By applying near-field imaging we | |
| can increase the spatial resolution to the dimensions of the laser spot size in | |
| the micrometer scale. For this purpose, the spintronic emitter is directly | |
| evaporated on a gold test pattern separated by a 300 nm spacer layer. Moving | |
| these structures with respect to the femtosecond laser spot which generates the | |
| THz radiation allows for resolution determination using the knife-edge method. | |
| We observe a full-width half-maximum THz beam diameter of $4.9(4){\mu}$m at 1 | |
| THz. The possibility to deposit spintronic emitter heterostructures on simple | |
| glass substrates makes them an interesting candidate for near-field imaging for | |
| a large number of applications.",2111.05023v1 | |