Combined Molecular and Spin Dynamics Simulation of BCC Iron with Vacancy Defects

TL;DR

This study uses combined molecular and spin dynamics simulations to analyze how vacancy defects affect spin wave excitations in ferromagnetic iron, revealing decreased frequencies, shorter lifetimes, and localized excitations near defects.

Contribution

It introduces a novel atomistic model that simultaneously handles translational and spin degrees of freedom to study vacancy effects on spin dynamics in iron.

Findings

Vacancy defects decrease spin wave frequencies and lifetimes.

Localized excitations occur near defect sites, increasing magnon scattering.

Spin wave peaks become less distinct with higher vacancy concentration.

Abstract

Utilizing an atomistic computational model which handles both translational and spin degrees of freedom, combined molecular and spin dynamics simulations have been performed to investigate the effect of vacancy defects on spin wave excitations in ferromagnetic iron. Fourier transforms of space and time-displaced correlation functions yield the dynamic structure factor, providing characteristic frequencies and lifetimes of the spin wave modes. Comparison of the system with a 5% vacancy concentration with pure lattice data shows a decrease in frequency as well as a decrease in lifetime for all transverse spin wave excitations observed. Additionally, a rugged spin wave line shape for low-q spin waves indicates the presence of multiple localized excitations near defect sites resulting in reduced excitation lifetimes due to increased magnon-magnon scattering. We observe further evidence of increased magnon-magnon scattering as the peaks in the longitudinal spin wave spectrum become less distinct.