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arXiv 1804.05947cond-mat.mes-hall
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Pt/Co和Pd/Co双层膜中自旋-轨道力矩角依赖性的第一性原理研究

First Principles Study of Angular Dependence of Spin-Orbit Torque in Pt/Co and Pd/Co Bilayers

Farzad Mahfouzi, Nicholas Kioussis

摘要:

近年来,在重金属(HM)/铁磁(FM)双层膜中,由于自旋霍尔效应和界面效应引起的自旋轨道矩(SOT)被用来通过面内电流注入实现磁化方向的切换.本文利用Keldysh Green函数方法和第一性原理电子结构计算,确定了HM/Co(HM = Pt,Pd)双层膜的类场(FL)和类阻尼(DL)SOT分量。我们的方法产生的FL和DL-SOT的磁化方向上的角度依赖性,而不假设先验的角度形式。SOT分解成费米海和费米面的贡献表明,SOT是由后者占主导地位。由于Co和HM之间的大晶格失配,我们还确定了拉伸双轴应变对FL和DL-SOT组件的影响。计算的FL-和DL-SOT的HM厚度的依赖性是总体上与实验吻合良好。SOT与费米能级位置的关系表明,DL-SOT主要由体HM的自旋霍尔效应决定。

英文摘要:

Spin-orbit torque (SOT) induced by spin Hall and interfacial effects in heavy metal(HM)/ferromagnetic(FM) bilayers has recently been employed to switch the magnetization direction using in-plane current injection. In this paper, using the Keldysh Green's function approach and first principles electronic structure calculations we determine the Field-Like (FL) and Damping-Like (DL) components of the SOT for the HM/Co (HM = Pt, Pd) bilayers. Our approach yields the angular dependence of both the FL- and DL-SOT on the magnetization direction without assuming a priori their angular form. Decomposition of the SOT into the Fermi sea and Fermi surface contributions reveals that the SOT is dominated by the latter. Due to the large lattice mismatch between the Co and the HM we have also determined the effect of tensile biaxial strain on both the FL- and DL-SOT components. The calculated dependence of FL- and DL-SOT on the HM thickness is overall in good agreement with experiment. The dependence of the SOT with the position of the Fermi level suggests that the DL-SOT dominated by the Spin Hall effect of the bulk HM.

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