Another view on Gilbert damping in two-dimensional ferromagnets

TL;DR

This paper develops a microscopic Kubo-Streda formalism to analyze Gilbert damping in 2D Rashba ferromagnets, revealing linear dependence on scattering rate and temperature robustness without vibrational effects.

Contribution

It introduces a microscopic approach to Gilbert damping, deriving an explicit formula for the damping tensor in 2D ferromagnets with spin-orbit coupling.

Findings

Gilbert damping parameter shows linear dependence on scattering rate.

Damping remains constant up to room temperature without vibrational effects.

Methodology applicable to metal bilayers like CoPt.

Abstract

A keen interest towards technological implications of spin-orbit driven magnetization dynamics requests a proper theoretical description, especially in the context of a microscopic framework, to be developed. Indeed, magnetization dynamics is so far approached within Landau-Lifshitz-Gilbert equation which characterizes torques on magnetization on purely phenomenological grounds. Particularly, spin-orbit coupling does not respect spin conservation, leading thus to angular momentum transfer to lattice and damping as a result. This mechanism is accounted by the Gilbert damping torque which describes relaxation of the magnetization to equilibrium. In this study we work out a microscopic Kubo-St\v{r}eda formula for the components of the Gilbert damping tensor and apply the elaborated formalism to a two-dimensional Rashba ferromagnet in the weak disorder limit. We show that an exact analytical expression corresponding to the Gilbert damping parameter manifests linear dependence on the scattering rate and retains the constant value up to room temperature when no vibrational degrees of freedom are present in the system. We argue that the methodology developed in this paper can be safely applied to bilayers made of non- and ferromagnetic metals, e.g., CoPt.