An excitation of a large-amplitude out-of-plane magnetization oscillation in a ferromagnet by the spin Hall effect is of great interest for practical applications such as microwave generator and neuromorphic computing. However, both experimental and theoretical works have revealed that only small-amplitude oscillation around an in-plane easy axis can be excited via the spin Hall effect. Here, we propose that an out-of-plane oscillation can be excited due to an assistance of field-like torque. We focus on an in-plane magnetized ferromagnet with an easy axis parallel to current direction. We notice that the field-like torque with an appropriate sign provides an additional field modifying the dynamic trajectory of the magnetization and drives the auto-oscillation. The condition on the sign of the field-like torque is satisfied for typical nonmagnet used in spin Hall devices such as tungsten.
Control of magnetization dynamics by spin Nernst torque
磁化动力学的控制是自旋电子学的主要目标之一。自旋霍尔效应（spin Hall effect）是指在非磁性金属（如Pt、W等）中利用自旋霍尔效应（spin Hall effect）将电荷流转化为自旋电流。在这项工作中，我们证明了Pt/Py双层中自旋能斯特矩对磁化强度的控制。我们通过测量在恒定加热或充电电流作用下磁力线宽度的系统变化，比较了自旋能斯特矩和自旋霍尔矩的相对强度。采用自旋力矩铁磁共振（ST-FMR）技术对磁体进行激励，并通过对称和反对称电压分量精确测量线宽。通过自旋能斯特力矩控制磁化动力学将成为操纵纳米磁体的另一种方式。
Layer-selective detection of magnetization directions from two layers of antiferromagnetically-coupled magnetizations by ferromagnetic resonance using a spin-torque oscillator
Measurements of spin-orbit torques in a ferromagnetic/nonmagnetic multilayer are typically based on an assumption that the entire ferromagnetic layer uniformly responds to the spin-orbit torque. This assumption breaks down when the thickness of the ferromagnetic layer is comparable to the dynamic exchange coupling length, which can be as short as a few nanometers in certain measurement geometries. The nonuniform magnetization reorientation coupled with nonuniform contribution of each magnetic sublayer to the magnetoresistance or the Kerr effect may impact the accuracy in the extrapolation of s…
We proposed and demonstrated a simple method for detection of in-plane magnetization switching by spin-orbit torque (SOT) in bilayers of non-magnetic / magnetic materials. In our method, SOT is used not only for magnetization switching but also for detection. Our method can detect arbitrary Mx and My component without an external magnetic field, which is useful for fast characterization of type-X, type-Y, and type-XY SOT magnetization switching. Our SOT detection scheme can be utilized not only for fast characterization of SOT switching in bilayers, but also for electrical detection of in-plan…
Both applied electric currents and magnetization dynamics modify the Dzyaloshinskii-Moriya interaction (DMI), which we call current-induced DMI (CIDMI) and dynamical DMI (DDMI), respectively. We report a theory of CIDMI and DDMI. The inverse of CIDMI consists in charge pumping by a time-dependent gradient of magnetization $\partial^2 M(r,t)/\partial r\partial t$, while the inverse of DDMI describes the torque generated by $\partial^2 M(r,t)/\partial r\partial t$. In noncollinear magnets CIDMI and DDMI depend on the local magnetization direction. The resulting spatial gradients correspond to to…
Universality of thermally assisted magnetic domain wall motion under spin torque
从理论上研究了自旋力矩作用下磁畴壁的热辅助运动。它示出的壁速度$v$指数依赖于自旋电流，$\Is$，低于阈值，以相同的方式在热激活运动驱动的力。低温下自旋力矩驱动情况的一个新特性是自旋电流中的线性项是普适的，即，$\ln v \sim \frac{π\hbar}{2e}(\Is/\kB T)$。这种行为，这是独立的钉扎和材料常数，可以用来证实实验上的自旋扭矩作为驱动机制。
We show that ideal memristors - devices whose resistance is proportional to the charge that flows through them - can be realized using spin torque-driven viscous magnetization dynamics. The latter can be accomplished in the spin liquid state of thin-film heterostructures with frustrated exchange, where memristive response is tunable by proximity to the glass transition, while current-induced Joule heating facilitates nonvolatile operation and second-order memristive functionality beneficial for neuromorphic applications. Ideal memristive behaviors can be achieved in other systems characterized…
Reply to Comment on "Acoustically assisted spin-transfer-torque switching of nanomagnets: An energy-efficient hybrid writing scheme for non-volatile memory" [Appl. Phys. Lett., 103, 232401 (2013)]
Parametric mechanism of the magnetization reversal as a low-power recording mechanism for MRAM. Measurement of spin-accumulation-induced in-plane magnetic field in a FeB nanomagnet
Current-induced switching of magnetic tunnel junctions: Effects of field-like spin-transfer torque, pinned-layer magnetization orientation and temperature
Reducing energy dissipation while increasing speed in computation and memory is a long-standing challenge for spintronics research. In the last 20 years, femtosecond lasers have emerged as a tool to control the magnetization in specific magnetic materials at the picosecond timescale. However, the use of ultrafast optics in integrated circuits and memories would require a major paradigm shift. An ultrafast electrical control of the magnetization is far preferable for integrated systems. Here we demonstrate reliable and deterministic control of the out-of-plane magnetization of a 1 nm-thick Co l…
Energy dissipation and switching delay in spin-transfer torque switching of nanomagnets with low-saturation magnetization in the presence of thermal fluctuations
Electric-field control of magnetization dynamics is fundamentally and technologically important for future spintronic devices. Here, based on electric-field control of both magnetic anisotropy and spin--orbit torque, two distinct methods are presented for switching the magnetization in topological insulator (TI)/magnetic-TI hybrid systems. The magnetic anisotropy energy in magnetic TIs is formulated analytically as a function of the Fermi energy, and it is confirmed that the out-of-plane magnetization is always favored for the partially occupied surface band. Also proposed is a transistor-like…
研究了富过渡金属（TM）和富稀土（RE）两种结构的亚铁磁性Gd $_x$（Fe $_{90}$ Co $_{10}$）$_{100-x}$薄膜的自旋-轨道转矩开关。自旋-轨道扭矩驱动的磁化切换遵循相同的偏手性在TM-丰富和RE-丰富的样品相对于总磁化，但偏手性的切换是相反的相对于TM磁化。这表明自旋-轨道-转矩驱动的磁切换的符号遵循总磁化，尽管基于输运的技术（诸如异常霍尔效应）仅对过渡金属磁化敏感。这些结果为研究反铁磁耦合亚晶格材料中自旋角动量转移的物理性质提供了重要的理论依据。
The reversal of perpendicular magnetization (PM) by electric control is crucial for high-density integration of low-power magnetic random-access memory (MRAM). Although the spin-transfer torque (STT) and spin-orbit torque (SOT) technologies have been used to switch the magnetization of a free layer with perpendicular magnetic anisotropy, the former has limited endurance because of the high current density directly through the junction, while the latter requires an external magnetic field or unconventional configuration to break the symmetry. Here we propose and realize the orbit-transfer torqu…
We study the effects of the coupling between magnetization dynamics and the electronic degrees of freedom in a heterostructure of a metallic nanomagnet with dynamic magnetization coupled with a superconductor containing a steady spin-splitting field. We predict how this system exhibits a non-linear spin torque, which can be driven either with a temperature difference or a voltage across the interface. We generalize this notion to arbitrary magnetization precession by deriving a Keldysh action for the interface, describing the coupled charge, heat and spin transport in the presence of a precess…
