Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore, 117583, Singapore.
Data Storage Institute, A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, 08-01 Innovis, Singapore, 138634, Singapore.
Sci Rep. 2016 May 17;6:26180. doi: 10.1038/srep26180.
Extensive efforts have been devoted to the study of spin-orbit torque in ferromagnetic metal/heavy metal bilayers and exploitation of it for magnetization switching using an in-plane current. As the spin-orbit torque is inversely proportional to the thickness of the ferromagnetic layer, sizable effect has only been realized in bilayers with an ultrathin ferromagnetic layer. Here we demonstrate that, by stacking ultrathin Pt and FeMn alternately, both ferromagnetic properties and current induced spin-orbit torque can be achieved in FeMn/Pt multilayers without any constraint on its total thickness. The critical behavior of these multilayers follows closely three-dimensional Heisenberg model with a finite Curie temperature distribution. The spin torque effective field is about 4 times larger than that of NiFe/Pt bilayer with a same equivalent NiFe thickness. The self-current generated spin torque is able to switch the magnetization reversibly without the need for an external field or a thick heavy metal layer. The removal of both thickness constraint and necessity of using an adjacent heavy metal layer opens new possibilities for exploiting spin-orbit torque for practical applications.
人们已经投入了大量的精力来研究铁磁金属/重金属双层中的自旋轨道扭矩，并利用平面电流来实现其用于磁化切换。由于自旋轨道扭矩与铁磁层的厚度成反比，因此仅在具有超薄铁磁层的双层中才实现了相当大的效果。在这里，我们证明通过交替堆叠超薄的 Pt 和 FeMn，可以在 FeMn/Pt 多层膜中实现铁磁性质和电流诱导的自旋轨道扭矩，而不会对其总厚度施加任何限制。这些多层膜的临界行为非常接近具有有限居里温度分布的三维海森堡模型。自旋扭矩有效场大约是具有相同等效 NiFe 厚度的 NiFe/Pt 双层的 4 倍。自生电流产生的自旋扭矩能够在无需外部磁场或厚重金属层的情况下可逆地切换磁化。去除厚度限制和使用相邻重金属层的必要性为实际应用中利用自旋轨道扭矩开辟了新的可能性。
