The Einstein-de Haas Effect in an $\textrm{Fe}_{15}$ Cluster

TL;DR

This paper presents a quantum-mechanically informed, time-dependent tight binding model that successfully simulates the Einstein-de Haas effect in an Fe cluster, highlighting the importance of spin-orbit coupling.

Contribution

It introduces a novel non-collinear tight binding model with spin-orbit coupling capable of simulating the Einstein-de Haas effect from first principles.

Findings

SOC is essential for angular momentum transfer at realistic fields.

The model captures adiabatic response timescales.

Simulations demonstrate the Einstein-de Haas effect in Fe clusters.

Abstract

Classical models of spin-lattice coupling are at present unable to accurately reproduce results for numerous properties of ferromagnetic materials, such as heat transport coefficients or the sudden collapse of the magnetic moment in hcp-Fe under pressure. This inability has been attributed to the absence of a proper treatment of effects that are inherently quantum mechanical in nature, notably spin-orbit coupling. This paper introduces a time-dependent, non-collinear tight binding model, complete with spin-orbit coupling and vector Stoner exchange terms, that is capable of simulating the Einstein-de Haas effect in a ferromagnetic $\textrm{Fe}_{15}$ cluster. The tight binding model is used to investigate the adiabaticity timescales that determine the response of the orbital and spin angular momenta to a rotating, externally applied $B$ field, and we show that the qualitative behaviours of our simulations can be extrapolated to realistic timescales by use of the adiabatic theorem. An analysis of the trends in the torque contributions with respect to the field strength demonstrates that SOC is necessary to observe a transfer of angular momentum from the electrons to the nuclei at experimentally realistic $B$ fields. The simulations presented in this paper demonstrate the Einstein-de Haas effect from first principles using a Fe cluster.