Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
Phys Rev Lett. 2015 Sep 18;115(12):127201. doi: 10.1103/PhysRevLett.115.127201. Epub 2015 Sep 14.
We demonstrate that spin-orbit coupled electrons in a magnetically doped system exert a spin torque on the local magnetization, without a flowing current, when the chemical potential is modulated in a magnetic field. The spin torque is proportional to the anomalous Hall conductivity, and its effective field strength may overcome the Zeeman field. Using this effect, the direction of the local magnetization is switched by gate control in a thin film. This charge-induced spin torque is essentially an equilibrium effect, in contrast to the conventional current-induced spin-orbit torque, and, thus, devices using this operating principle possibly have higher efficiency than the conventional ones. In addition to a comprehensive phenomenological derivation, we present a physical understanding based on a model of a Dirac-Weyl semimetal, possibly realized in a magnetically doped topological insulator. The effect might be realized also in nanoscale transition materials, complex oxide ferromagnets, and dilute magnetic semiconductors.
我们证明了当磁场中化学势调制时，磁掺杂系统中的自旋轨道耦合电子在没有流动电流的情况下会对局部磁化施加自旋力矩。自旋力矩与反常霍尔电导率成正比，其有效场强可能超过塞曼场。利用这一效应，通过在薄膜中的栅极控制来切换局部磁化的方向。与传统的电流诱导自旋轨道力矩相比，这种电荷诱导的自旋力矩本质上是一种平衡效应，因此，采用这种工作原理的器件可能比传统器件具有更高的效率。除了全面的唯象推导外，我们还基于狄拉克-外尔半金属模型提出了一种物理理解，该模型可能在磁掺杂拓扑绝缘体中实现。这种效应也可能在纳米级过渡材料、复合氧化物铁磁体和稀磁半导体中实现。
