Bath-induced spin inertia

TL;DR

This paper reveals that coupling a macrospin to its environment (bath) induces spin inertia, challenging the traditional view of spin dynamics as inertia-free, and provides a theoretical framework for understanding recent experimental observations.

Contribution

It introduces the concept of bath-induced spin inertia, showing its universal emergence from high-frequency bath modes and its implications for spin dissipation and dynamics modeling.

Findings

Bath coupling causes universal spin inertia from high-frequency modes.

Spin inertia influences spin dissipation channels.

Application to phonon bath in YIG/GGG stack demonstrates the effect.

Abstract

Spin dynamics is usually described as massless or, more precisely, as free of inertia. Recent experiments, however, found direct evidence for inertial spin dynamics. In turn, it is necessary to rethink the basics of spin dynamics. Focusing on a macrospin in an environment (bath), we show that the spin-to-bath coupling gives rise to spin inertia. This bath-induced spin inertia appears universally from all the high-frequency bath modes. We expect our results to provide new insights into recent experiments on spin inertia. Moreover, they indicate that any channel for spin dissipation should also be accompanied by a term accounting for bath-induced spin inertia. As an illustrative example, we consider phonon-bath-induced spin inertia in a YIG/GGG stack.