Electrical control of magnetization is of crucial importance for integrated spintronics devices. Spin-orbit torques (SOT) in heavy-metal/ferromagnetic heterostructures have emerged as a promising tool to achieve efficiently current-induced magnetization reversal. However, the microscopic origin of the SOT is being debated, with the spin Hall effect (SHE) due to nonlocal spin currents and the spin Rashba-Edelstein effect (SREE) due to local spin polarization at the interface being the primary candidates. We investigate the electrically induced out-of-equilibrium spin and orbital polarizations in pure Pt films and in Pt/$3d$-metal (Co, Ni, Cu) bilayer films using ab initio electronic structure methods and linear-response theory. We compute atom-resolved response quantities that allow us to identify the induced spin-polarization contributions that lead to fieldlike (FL) SOTs, mostly associated with the SREE, and dampinglike (DL) SOTs, mostly associated with the SHE, and compare their relative magnitude, dependence on the magnetization direction, as well as their Pt-layer thickness dependence. We find that both the FL and DL components contribute to the resulting SOT at the Pt/Co and Pt/Ni interfaces, with the former contributions being larger at the Pt interface layer and the latter larger in the Co or Ni layers. Our calculations show that the electrically induced transverse orbital polarization is exceedingly larger than the induced spin polarization and present even without spin-orbit coupling, in contrast to the spin polarization.

中文翻译：

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重金属/3d-金属双层中电致自旋和轨道极化的定量比较

磁化的电控制对于集成自旋电子器件至关重要。重金属/铁磁异质结构中的自旋轨道扭矩 (SOT) 已成为有效实现电流感应磁化反转的有前途的工具。然而，SOT 的微观起源正在争论中，由非局部自旋电流引起的自旋霍尔效应 (SHE) 和由于界面处局部自旋极化引起的自旋 Rashba-Edelstein 效应 (SREE) 是主要候选者。我们研究了纯 Pt 薄膜和 Pt/$3d$- 使用ab initio 的金属（Co、Ni、Cu）双层膜电子结构方法和线性响应理论。我们计算原子分辨响应量，使我们能够识别导致场状 (FL) SOT 的诱导自旋极化贡献，主要与 SREE 相关，以及类阻尼 (DL) SOT，主要与 SHE 相关，并比较它们的相对大小，对磁化方向的依赖性，以及它们的 Pt 层厚度依赖性。我们发现 FL 和 DL 分量都对 Pt/Co 和 Pt/Ni 界面处的 SOT 有贡献，前者在 Pt 界面层的贡献更大，而后者在 Co 或 Ni 层的贡献更大。我们的计算表明，电诱导的横向轨道极化远大于诱导的自旋极化，并且即使没有自旋轨道耦合也存在，