Ma Qinli, Li Yufan, Gopman D B, Kabanov Yu P, Shull R D, Chien C L
Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
Phys Rev Lett. 2018 Mar 16;120(11):117703. doi: 10.1103/PhysRevLett.120.117703.
An ultimate goal of spintronics is to control magnetism via electrical means. One promising way is to utilize a current-induced spin-orbit torque (SOT) originating from the strong spin-orbit coupling in heavy metals and their interfaces to switch a single perpendicularly magnetized ferromagnetic layer at room temperature. However, experimental realization of SOT switching to date requires an additional in-plane magnetic field, or other more complex measures, thus severely limiting its prospects. Here we present a novel structure consisting of two heavy metals that delivers competing spin currents of opposite spin indices. Instead of just canceling the pure spin current and the associated SOTs as one expects and corroborated by the widely accepted SOTs, such devices manifest the ability to switch the perpendicular CoFeB magnetization solely with an in-plane current without any magnetic field. Magnetic domain imaging reveals selective asymmetrical domain wall motion under a current. Our discovery not only paves the way for the application of SOT in nonvolatile technologies, but also poses questions on the underlying mechanism of the commonly believed SOT-induced switching phenomenon.
自旋电子学的一个终极目标是通过电学手段控制磁性。一种很有前景的方法是利用源自重金属及其界面处强自旋轨道耦合的电流诱导自旋轨道矩（SOT），在室温下切换单个垂直磁化的铁磁层。然而，迄今为止，SOT 切换的实验实现需要一个额外的面内磁场或其他更复杂的措施，从而严重限制了其前景。在此，我们展示了一种由两种重金属组成的新型结构，该结构能产生具有相反自旋指数的相互竞争的自旋电流。与人们预期的以及被广泛接受的 SOT 所证实的那样，仅仅抵消纯自旋电流和相关的 SOT 不同，此类器件展现出仅通过面内电流而无需任何磁场就能切换垂直 CoFeB 磁化的能力。磁畴成像揭示了电流作用下选择性的不对称畴壁运动。我们的发现不仅为 SOT 在非易失性技术中的应用铺平了道路，也对普遍认为的 SOT 诱导开关现象的潜在机制提出了质疑。
