Current-induced Spin-Orbit Torques

Spin-orbit torques (SOTs) describe the current-induced magnetic torques originating from the spin-orbit coupling of conduction electrons in the bulk and interfaces of materials. First demonstrated experimentally in semiconductors and then in metals, SOTs have attracted enormous attention from the spintronics and community due to their immense potential and flexibility in manipulating magnetization by electricity.

Over the past decade, a handful of  SOT generating mechanisms have been discovered, including the spin Hall effect (SHE), interfacial Rashba–Edelstein effect, topological surface and bulk states, etc. Among these, the SHE is primarily considered as a SOT source for current-induced magnetization manipulation in ferrimagnetic garnets, of interest to our project. The SHE emerges in the bulk of the materials characterized by strong spin-orbit coupling (e.g., Pt, W, and Ta) and describes the spin-dependent scattering of conduction electrons, generating a pure spin current transverse to the charge current injection direction. A magnetic layer in interfacial contact with a SHE material can then absorb the resulting spin current, which acts as a spin-torque on the magnetization and enables its reversal. While the spin current generation mechanism differs in the other listed SOT sources, the applied torque has comparable symmetry.