We demonstrate a tunable spin–orbit torque (SOT) switching in an antiferromagnetically coupled CoFeB/Ta/CoFeB trilayer through careful design of magnetic anisotropies, where the thicker bottom CoFeB layer has a relatively weak perpendicular magnetic anisotropy (PMA) and PMA of the upper CoFeB layer is robust. The unique anisotropy feature causes a strong sensitivity to the assistant field during SOT switching, resulting in a slanted magnetic moment and a highly tunable switching window defined by the difference in Hall resistance between two SOT switching states at zero current. By further reducing the PMA of bottom CoFeB, only the upper layer can be switched by SOT. Until now, there are three types of SOT switching in antiferromagnetically coupled ferromagnetic metal/nonmagnetic metal/ferromagnetic metal trilayers: simultaneous switching between two antiparallel states with strong PMA for both ferromagnetic layers, field-free switching where one layer has in-plane magnetization and the other has canted out-of-plane magnetization, and tunable switching reported in this work. Our findings enrich the physical phenomena in trilayer SOT and may have potential application in multilevel storage and neural computing.

中文翻译：

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反铁磁耦合 CoFeB/Ta/CoFeB 中的可调自旋轨道扭矩切换

我们通过精心设计的磁各向异性证明了反铁磁耦合的 CoFeB/Ta/CoFeB 三层中的可调自旋轨道扭矩 (SOT) 切换，其中较厚的底部 CoFeB 层具有相对较弱的垂直磁各向异性 (PMA) 和上部的 PMA CoFeB 层坚固耐用。独特的各向异性特征在 SOT 开关期间对辅助场产生很强的敏感性，从而产生倾斜的磁矩和高度可调的开关窗口，开关窗口由零电流下两个 SOT 开关状态之间的霍尔电阻差异定义。通过进一步降低底部 CoFeB 的 PMA，SOT 只能切换上层。到目前为止，反铁磁耦合铁磁金属/非磁金属/铁磁金属三层中的 SOT 切换有以下三种类型：在两个反平行状态之间同时切换，两个铁磁层都具有强 PMA，无场切换，其中一层具有面内磁化，另一层具有倾斜的面外磁化，以及这项工作中报道的可调切换。我们的发现丰富了三层 SOT 中的物理现象，并可能在多级存储和神经计算中具有潜在应用。