Tuning spin-orbit torques across the phase transition in VO$_2$/NiFe heterostructure
Jun-young Kim, Joel Cramer, Kyujoon Lee, Dong-Soo Han, Dongwook Go, Pavel Salev, Pavel N. Papa, Nicolas M. Vargas, Ivan K. Schuller, Yuriy Mokrousov, Gerhard Jakob, Mathias Kläui
The emergence of spin-orbit torques as a promising approach to energy-efficient magnetic switching has generated large interest in material systems with easily and fully tunable spin-orbit torques. Here, current-induced spin-orbit torques in VO$_2$/NiFe heterostructures were investigated using spin-torque ferromagnetic resonance, where the VO$_2$ layer undergoes a prominent insulator-metal transition. A roughly two-fold increase in the Gilbert damping parameter, $α$, with temperature was attributed to the change in the VO$_2$/NiFe interface spin absorption across the VO$_2$ phase transition. More remarkably, a large modulation ($\pm$100%) and a sign change of the current-induced spin-orbit torque across the VO$_2$ phase transition suggest two competing spin-orbit torque generating mechanisms. The bulk spin Hall effect in metallic VO$_2$, corroborated by our first-principles calculation of spin Hall conductivity, $σ_{SH} \approx 10^4 \frac{\hbar}{e} Ω^{-1} m^{-1}$, is verified as the main source of the spin-orbit torque in the metallic phase. The self-induced/anomalous torque in NiFe, of the opposite sign and a similar magnitude to the bulk spin Hall effect in metallic VO$_2$, could be the other competing mechanism that dominates as temperature decreases. For applications, the strong tunability of the torque strength and direction opens a new route to tailor spin-orbit torques of materials which undergo phase transitions for new device functionalities.
The 5d transition-metal oxides have a unique electronic structure dominated by strong spin-orbit coupling and hence they can be an intriguing platform to explore spin-current physics. Here, we report on room-temperature generation of spin-orbit torque (SOT) from a conductive 5d iridium oxide, IrO2. By measuring second-harmonic Hall resistance of Ni81Fe19/IrO2 bilayers, we find both dampinglike and fieldlike SOTs. The former is larger than the latter, enabling easier control of magnetization. We also observe that the dampinglike SOT efficiency has a significant dependence on IrO2 thickness, whi…
Interfacial spin-orbit torque without bulk spin-orbit coupling
存在自旋-轨道耦合时的电流可以产生自旋累积，其对附近的磁化施加转矩。我们证明，即使在没有材料与强大的体自旋轨道耦合，扭矩可以出现仅仅是由于界面自旋轨道耦合，即Rashba-Eldestein效应在金属/绝缘体界面。在夹在弱自旋轨道金属（Ti）和绝缘体（Al $_2$ O $_3$）之间的软磁NiFe中，该扭矩表现为有效场，其显著大于奥斯特场并且对在NiFe和Al $_2$ O $_3$之间插入附加层敏感。我们的研究结果指出了通过工程界面电偶极子调整自旋轨道扭矩的新途径。
Spin-Orbital Hall Nano-Oscillators using PtCr/NiFe
University of Gothenburg（哥德堡大学）；Tohoku University（东北大学）；Uppsala University（乌普萨拉大学）；Vietnam Academy of Science and Technology（越南科学技术院）；Chalmers University of Technology（查尔姆斯理工大学）
Harnessing Native Chromium Oxidation for Giant Orbital Torque and Field-Free Magnetization Switching in NiFe/Cr Bilayers
Indian Institute of Technology Ropar（印度理工学院罗帕尔分校）；Indian Institute of Technology Mandi（印度理工学院曼迪分校）；Indian Institute of Technology Bhubaneswar（印度理工学院布巴内斯瓦尔分校）；Virginia Commonwealth University（弗吉尼亚联邦大学）；Jaypee Institute of Information Technology（贾伊皮信息技术学院）
We report in this study the current-induced-torque excitation of acoustic and optical modes in Ta/NiFe/Ru/NiFe/Ta synthetic antiferromagnet stacks grown on SiO2/Si substrates. The two Ta layers serve as spin torque sources with the opposite polarisations both in spin currents and Oersted fields acting on their adjacent NiFe layers. This can create the odd symmetry of spatial spin torque distribution across the growth direction, allowing us to observe different spin-wave excitation efficiency from synthetic antiferromagnets excited by homogeneous torques. We analyse the torque symmetry by in-pl…
The manipulation of magnetization in a metallic ferromagnet by using optical helicity has been much attracted attention for future opto-spintronic devices. The optical helicity induced torques on the magnetization, {\it optical spin torque}, have been observed in ferromagnetic thin films recently. However, the interfacial effect of the optical spin torque in ferromagnet/nonmagnetic heavy metal heterostructures have not been addressed so far, which are widely utilized to efficiently control magnetization via electrical means. Here, we studied optical spin torque vectors in the ferromagnet/nonma…
A large anti-damping spin-obit torque (SOT) efficiency in magnetic heterostructures is a prerequisite to realize energy efficient spin torque based magnetic memories and logic devices. The efficiency can be characterized in terms of the spin-orbit fields generated by anti-damping torques when an electric current is passed through the non-magnetic layer. We report a giant spin-orbit field of 48.96 (27.50) mT at an applied current density of 1 MAcm-2 in beta-W interfaced Co60Fe40 (Ni81Fe19)/TiN epitaxial structures due to an anti-damping like torque, which results in a magnetization auto-oscilla…
Tunable Spin-Orbit Torques in Cu-Ta Binary Alloy Heterostructures
发现自旋霍尔效应（SHE）在重过渡金属（HM）（诸如Ta和W）中在它们的非晶和/或高电阻率形式下是强的。在这项工作中，我们表明，通过采用Cu-Ta二元合金作为缓冲层的非晶Cu $_{100-x}$ Ta $_{x}$基磁性异质结构的垂直磁各向异性（PMA），SHE诱导的阻尼类自旋-轨道扭矩（DL-SOT）效率$|ξ_{DL}|$可以通过调节缓冲层的电阻率线性调谐。电流感应SOT开关也可以实现在这些Cu $_{100-x}$ Ta $_{x}$为基础的磁性异质结构，我们发现更好地解释了SOT辅助畴壁传播图片的开关行为。通过对不同组成的Cu $_{100-x}$ Ta $_{x}$基样品的系统研究，确定了富Ta区自旋霍尔电导率$|σ_{SH}|\approx2.02\times10^{4}[\hbar/2e]Ω^{-1}\cdot\operatorname{m}^{-1}$的下限。基于电阻率调谐的思想，我们进一步证明，$|ξ_{DL}|$可以提高从0.087纯钽到0.152，通过采用电阻TaN缓冲层。
A Comparative Study on Spin-Orbit Torque Efficiencies from W/ferromagnetic and W/ferrimagnetic Heterostructures
它已被证明，W在其电阻形式具有最大的自旋霍尔比在所有重过渡金属，这使得它是一个很好的候选人产生有效的阻尼类自旋轨道扭矩（DL-SOT）作用于相邻的铁磁或亚铁磁（FM）层。在这里，我们提供了一个系统的研究的自旋输运性质的W/FM磁性异质结构的FM层是铁磁Co $_{20}$ Fe $_{60}$ B $_{20}$或亚铁磁Co $_{63}$ Tb $_{37}$与垂直磁各向异性。采用电流诱导磁滞回线法研究了W/Co $_{20}$ Fe $_{60}$ B $_{20}$和W/Co $_{63}$ Tb $_{37}$体系的DL-SOT效率$|ξ_{DL}|$与W缓冲层的微观结构之间的关系。在W/Co $_{20}$ Fe $_{60}$ B $_{20}$和W/Co $_{63}$ Tb $_{37}$异质结构中，当W层部分非晶时，分别获得最大值的$|ξ_{DL}|\approx 0.144$和$|ξ_{DL}|\approx 0.116$。我们的研究结果表明，自旋霍尔效应从电阻相的W可以被用来有效地控制铁磁和亚铁磁层通过DL-SOT机制。
Spin-orbit torque magnetization switching in MoTe2/permalloy heterostructures
通过自旋-轨道感应转矩来切换磁性元件的能力最近吸引了很多关注，以实现具有低功耗的高性能非易失性存储器。实现有效的基于自旋-轨道的切换需要利用新材料和新物理来获得高的电荷-自旋转换效率，因此使得自旋源的选择至关重要。在这里，我们报告的观察自旋-轨道转矩开关的双层组成的半金属膜的1 T '-MoTe 2相邻坡莫合金。确定性开关实现没有外部磁场在室温下，和开关发生的电流的一个数量级小于那些典型的设备使用性能最好的重金属。如果除了体自旋霍尔效应之外还考虑界面自旋-轨道贡献，则可以理解厚度依赖性。进一步减少三倍的开关电流证明与诉诸哑铃形的磁性元件。这些发现预示了MoTe 2在低功率半金属材料自旋器件中的应用前景。
Spin-orbit torque (SOT) provides an efficient way to achieve charge-to-spin conversion and can switch perpendicular magnetization, which is essential for designing novel energy-efficient spintronic devices. An out-of-plane SOT could directly switch perpendicular magnetization. Encouragingly, field-free perpendicular magnetization switching of a two-dimensional (2D) material WTe2/ferromagnet (FM) bilayer has been reported recently, but the working temperature (200 K) is below room temperature. Here, we report the field-free perpendicular magnetization switching carried out at room temperature o…
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 $β$-W/CoFeB layers. Fir…
Detailed and high-throughput measurement of composition dependence of magnetoresistance and spin-transfer torque using a composition-gradient film: application to Co$_{x}$Fe$_{1-x}$ (0 $\le$ $\textit{x}$ $\le$ 1) system
Topological insulators have emerged as an important material class for efficient spin-charge interconversion. Most topological insulators considered to date are binary or ternary compounds, with the exception of $α$-Sn. Here we report a comprehensive characterization of the growth, magnetotransport properties, and current-induced spin-orbit torques of $α$-Sn and $β$-Sn-based ferromagnetic heterostructures. We show that $α$-Sn grown with a Bi surfactant on CdTe(001) promotes large spin-orbit torques in a ferromagnetic FeCo layer at room temperature, comparable to Pt, whereas $α$-Sn grown withou…
Spin-orbit torque can drive electrical switching of magnetic layers. Here, we report that at least for micrometer-sized samples there is no simple correlation between the efficiency of dampinglike spin-orbit torque (ξ_DL^j) and the critical switching current density of perpendicularly magnetized spin-current generator/ferromagnet heterostructures. We find that the values of ξ_DL^j based on switching current densities can either under- or over-estimated ξ_DL^j by up to tens of times in a domain-wall depinning analysis, while in the macrospin analysis based on the switching current density ξ_DL^…
Electrical manipulation of magnetism via spin-orbit torques (SOTs) promises efficient spintronic devices. In systems comprising magnetic insulators and heavy metals, SOTs have started to be investigated only recently, especially in systems with interfacial Dzyaloshinskii-Moriya interaction (iDMI). Here, we quantitatively study the SOT efficiency and iDMI in a series of gadolinium gallium garnet (GGG) / thulium iron garnet (TmIG) / platinum (Pt) heterostructures with varying TmIG and Pt thicknesses. We find that the non-monotonic SOT efficiency as a function of the magnetic layer thickness is n…
Determination of the Spin-Hall-Effect-Induced and the Wedged-Structure-Induced Spin Torque Efficiencies in Heterostructures with Perpendicular Magnetic Anisotropy
Efficient Spin-Orbit Torque Switching with Non-Epitaxial Chalcogenide Heterostructures
近年来，拓扑绝缘体（TI）产生的自旋轨道矩（SOT）受到越来越多的关注。这些TI通常由外延生长的硫族化合物形成，具有极高的SOT效率，在下一代自旋电子器件中具有很大的潜力。然而，这些硫族化物的外延需要确保拓扑保护的表面态（TSS）的存在，这限制了在工业中使用这些材料的可行性。在这项工作中，我们表明，非外延的Bi $_{x}$ Te $_{1-x}$ /铁磁异质结制备的常规磁控溅射具有巨大的SOT效率，即使没有TSS。通过谐波电压测量和磁滞回线位移测量，我们发现这种非外延异质结构的体自旋轨道相互作用产生的类阻尼SOT效率在室温下可以达到大于100%的值。我们进一步证明了这些Bi $_{x}$ Te $_{1-x}$为基础的异质结构与热稳定的铁磁层，这表明，这种非外延硫族化物材料可以是潜在的有效的SOT源在未来的SOT磁存储器件的电流诱导SOT开关。
Dominant spin Hall torque and negligible orbital Hall torque in α-W/ferromagnet heterostructures with artifacts-free angular momentum detectors
State Key Laboratory of Semiconductor Physics and Chip Technologies, Institute of Semiconductors, Chinese Academy of Sciences（中国科学院半导体研究所半导体物理与芯片技术国家重点实验室）；Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences（中国科学院大学材料科学与光电工程技术研究中心）；College of Physics and Information Technology, Shaanxi Normal University（陕西师范大学物理学与信息技术学院）
