Non-equilibrium formulation of helicity-dependent thermal field for ultrafast magnetization dynamics

TL;DR

This paper introduces a non-equilibrium thermal field model for simulating ultrafast magnetization dynamics, accurately capturing demagnetization phenomena at femtosecond timescales.

Contribution

It proposes a novel non-equilibrium thermal field based on atomic spin flip probabilities, enabling grid-independent modeling of ultrafast demagnetization.

Findings

Successfully reproduces demagnetization for various cell sizes.

Achieves effective temperatures of thousands of Kelvin.

Provides a foundation for multiscale ultrafast magnetization modeling.

Abstract

Far-from-equilibrium magnetization dynamics can be accessed when a magnetic material is subject to a femtosecond excitation, such as an optical laser or an electric current. Numerically, the demagnetization of magnetic materials is typically modeled by atomistic spin dynamics. Micromagnetic models generally fail to reproduce ultrafast demagnetization in a grid independent manner. Here, we propose a non-equilibrium thermal field whose features depend on atomic spin flip probabilities. Under the assumption that each spin flip is equivalent to a quantum of angular momentum, equivalent temperatures on the order of thousands of Kelvin are achieved. Demagnetization is quantitatively reproduced for several cell sizes. The presented approach can be further refined and extended towards a grid-independent and multiscale modeling of ultrafast magnetization dynamics.