Fluctuations in Spin Dynamics Excited by Pulsed Light

TL;DR

This paper presents a theoretical study of nonequilibrium spin fluctuations in ferromagnets induced by pulsed light, introducing a new framework for analyzing spin noise and relaxation dynamics.

Contribution

It develops a Lindblad equation approach consistent with the Landau-Lifshitz-Gilbert equation to analyze spin fluctuations and introduces a Fano factor for nonequilibrium spin noise analysis.

Findings

Autocorrelation function includes thermal and nonequilibrium components

Fano factor provides insights into spin transfer to the environment

Framework enables nonequilibrium spin noise spectroscopy

Abstract

We theoretically investigate nonequilibrium spin fluctuations in a ferromagnet induced by a light pulse. Using a Lindblad equation consistent with the Landau-Lifshitz-Gilbert equation, we compute the autocorrelation function of magnetization. Our analysis reveals that this function comprises both thermal and nonequilibrium components. To examine the latter in detail, we introduce a Fano factor similar to nonequilibrium current noise in electronic circuits. We demonstrate that this factor encapsulates insights into the transfer of spin units to the environment. Our findings lay the groundwork for nonequilibrium spin noise spectroscopy, offering valuable insights into spin relaxation dynamics.