Microscopic theory of Gilbert damping in metallic ferromagnets

TL;DR

This paper develops a microscopic theory for magnetization relaxation in metallic nanostructures, accounting for spin-orbit coupling, and reveals limitations of traditional phenomenological models in such systems.

Contribution

It introduces a novel microscopic approach to calculate damping rates in perfectly crystalline metallic ferromagnets with spin-orbit coupling.

Findings

Damping rate depends on frequency in relevant regimes.

Standard Landau-Lifshitz-Gilbert model may be inadequate.

Method applicable to perfectly crystalline systems.

Abstract

We present a microscopic theory for magnetization relaxation in metallic ferromagnets of nanoscopic dimensions that is based on the dynamic spin response matrix in the presence of spin-orbit coupling. Our approach allows the calculation of the spin excitation damping rate even for perfectly crystalline systems, where existing microscopic approaches fail. We demonstrate that the relaxation properties are not completely determined by the transverse susceptibility alone, and that the damping rate has a non-negligible frequency dependence in experimentally relevant situations. Our results indicate that the standard Landau-Lifshitz-Gilbert phenomenology is not always appropriate to describe spin dynamics of metallic nanostructure in the presence of strong spin-orbit coupling.