Symmetry-dependent field-free switching of perpendicular magnetization
Symmetry-dependent field-free switching of perpendicular magnetization
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DOI：
10.1038/s41565-020-00826-8
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发表时间：
2021-01-18
影响因子：
38.3
通讯作者：
Chen, Jingsheng
中科院分区：
文献类型：
--
作者：
Liu, Liang;Zhou, Chenghang;Chen, Jingsheng
现代磁记忆技术要求实现垂直磁化的全电控制和低能耗。虽然重金属/铁磁体（HM/FM）异质结构（1-5）中的自旋轨道扭矩（SOT）在磁性随机存取存储器中的应用中具有希望，但直到今天，它仍限于平面内方向。这样的面内转矩可以仅借助于额外的对称性破坏来确定性地切换垂直磁化，例如通过施加外部磁场（2，4）、层间/交换耦合（6-9）或不对称设计（10-14）。相反，面外SOT 15可以直接切换垂直磁化。在这里，我们观察到的HM/FM双层的L1（1）有序的CuPt/CoPt的面外SOT和演示的CoPt层的垂直磁化的无场开关。在CuPt/CoPt界面处的低对称性点群（3 m1）引起该自旋扭矩，下文称为3 m扭矩，其强烈地依赖于电流的相对取向和晶体对称性。我们观察到一个三倍的角度依赖于无场开关和电流诱导的面外有效场。由于3 m转矩的固有性质，CuPt/CoPt中的无场切换在循环实验中显示出良好的耐久性。实验涉及各种各样的SOT双层低对称点群（16，17）在界面上可能会揭示进一步的非常规自旋扭矩在未来。
Modern magnetic-memory technology requires all-electric control of perpendicular magnetization with low energy consumption. While spin-orbit torque (SOT) in heavy metal/ferromagnet (HM/FM) heterostructures(1-5) holds promise for applications in magnetic random access memory, until today, it has been limited to the in-plane direction. Such in-plane torque can switch perpendicular magnetization only deterministically with the help of additional symmetry breaking, for example, through the application of an external magnetic field(2,4), an interlayer/exchange coupling(6-9) or an asymmetric design(10-14). Instead, an out-of-plane SOT15 could directly switch perpendicular magnetization. Here we observe an out-of-plane SOT in an HM/FM bilayer of L1(1)-ordered CuPt/CoPt and demonstrate field-free switching of the perpendicular magnetization of the CoPt layer. The low-symmetry point group (3m1) at the CuPt/CoPt interface gives rise to this spin torque, hereinafter referred to as 3m torque, which strongly depends on the relative orientation of the current flow and the crystal symmetry. We observe a three-fold angular dependence in both the field-free switching and the current-induced out-of-plane effective field. Because of the intrinsic nature of the 3m torque, the field-free switching in CuPt/CoPt shows good endurance in cycling experiments. Experiments involving a wide variety of SOT bilayers with low-symmetry point groups(16,17) at the interface may reveal further unconventional spin torques in the future.