Simulation of a spin-wave instability from atomistic spin dynamics

TL;DR

This paper investigates spin-wave instability in atomistic spin dynamics, revealing a non-dissipative relaxation mechanism that challenges the macro moment picture in uniaxial anisotropy conditions.

Contribution

It introduces the concept of spin-wave instability and demonstrates its effects through atomistic simulations, showing breakdown of macro moment approximation.

Findings

Spin-wave instability causes macro moment relaxation.

Relaxation can be non-dissipative and variable in size.

Macro moment picture breaks down under certain conditions.

Abstract

We study the spin dynamics of a Heisenberg model at finite temperature in the presence of an external field or a uniaxial anisotropy. For the case of the uniaxial anisotropy our simulations show that the macro moment picture breaks down. An effect which we refer to as a spin-wave instability (SWI) results in a non-dissipative Bloch-Bloembergen type relaxation of the macro moment where the size of the macro moment changes, and can even be made to disappear. This relaxation mechanism is studied in detail by means of atomistic spin dynamics simulations.