Simulation of the Einstein-de Haas effect combining molecular and spin dynamics

TL;DR

This study models the Einstein-de Haas effect in ferromagnetic nanoparticles by combining molecular and spin dynamics, demonstrating how anisotropy influences angular momentum transfer and relaxation times.

Contribution

It introduces a coupled spin-lattice dynamic model conserving total angular momentum and applies it to simulate the Einstein-de Haas effect in Fe nanoclusters.

Findings

Angular momentum transfer rate depends on magnetic anisotropy strength.

Full spin-lattice relaxation occurs within ~100 ps with realistic anisotropy energies.

The model conserves total angular momentum while allowing exchange between spin and lattice.

Abstract

The spin and lattice dynamics of a ferromagnetic nanoparticle are studied via molecular dynamics and with semi-classical spin dynamics simulations where spin and lattice degrees of freedom are coupled via a dynamic uniaxial anisotropy term. We show that this model conserves total angular momentum, whereas spin and lattice angular momentum are not conserved. We carry out simulations of the the Einstein-de Haas effect for a Fe nanocluster with more than 500 atoms that is free to rotate, using a modified version of the open-source spinlattice dynamics code (SPILADY). We show that the rate of angular momentum transfer between spin and lattice is proportional to the strength of the magnetic anisotropy interaction. The addition of the anisotropy allows full spin-lattice relaxation to be achieved on previously reported timescales of \sim 100 ps and for tight-binding magnetic anisotropy energies comparable to those of small Fe nanoclusters.