Magnetization Dynamics driven by Non-equilibrium Spin-Orbit Coupled Electron Gas

TL;DR

This paper develops a quantum density matrix approach to study how non-equilibrium spin accumulation and electron baths with spin-orbit coupling influence magnetization dynamics, revealing damping effects not captured by semi-classical models.

Contribution

It introduces a quantum theoretical framework for magnetization dynamics coupled to spin-orbit coupled electron gases, highlighting damping effects absent in previous semi-classical theories.

Findings

Non-equilibrium spin accumulation induces spin torque.

Electron bath causes damping comparable to Gilbert damping.

Damping effects are significant in magnetization dynamics.

Abstract

The dynamics of magnetization coupled to an electron gas via s-d exchange interaction is investigated by using density matrix technique. Our theory shows that non-equilibrium spin accumulation induces a spin torque and the electron bath leads to a damping of the magnetization. For the two-dimensional magnetization thin film coupled to the electron gas with Rashba spin-orbit coupling, the result for the spin-orbit torques is consistent with the previous semi-classical theory. Our theory predicts a damping of the magnetization, which is absent in the semi-classical theory. The magnitude of the damping due to the electron bath is comparable to the intrinsic Gilbert damping and may be important in describing the magnetization dynamics of the system.