Spin angular momentum transfer in the Einstein-de Haas effect

TL;DR

This paper elucidates how spin angular momentum is partitioned between phonons and rigid-body rotation during the Einstein-de Haas effect, revealing the dominant transfer to rotation and the critical role of phonons, with implications for magneto-mechanical control.

Contribution

It introduces a detailed microscopic analysis of angular momentum transfer in the Einstein-de Haas effect, highlighting the roles of phonons and rigid-body rotation and the influence of anisotropy and Dzyaloshinskii-Moriya interactions.

Findings

Rigid-body rotation acquires most of the angular momentum.

Phonons absorb most of the kinetic energy during transfer.

Anisotropy and Dzyaloshinskii-Moriya interactions modulate transfer dynamics.

Abstract

We investigate spin angular momentum transfer in the Einstein-de Haas effect within prototypical magnetic crystals, focusing on its partition between phonons and rigid-body rotation. Using the Eckart frame to decouple local vibrations (phonons) from rigid-body rotation, we demonstrate that spin angular momentum is simultaneously transferred into both phonons and rigid-body rotation in an asymmetric way: rigid-body rotation acquires the dominant share of angular momentum, while phonons absorb most of the resulting kinetic energy. This divergent transfer of angular momentum and energy identifies phonons as direct and indispensable participants in the Einstein-de Haas dynamics. Furthermore, we find that pseudo-dipolar anisotropy and Dzyaloshinskii-Moriya interaction exert distinct control over the angular momentum transfer. Stronger pseudo-dipolar anisotropy increases the total amount of transferred angular momentum, whereas stronger Dzyaloshinskii-Moriya interaction accelerates the transfer rate and increases the proportion of phonon angular momentum. Our work clarifies the microscopic picture of the Einstein-de Haas effect and enables targeted angular-momentum control in magneto-mechanical devices.