Driving Force of Ultrafast Magnetization Dynamics

TL;DR

This paper models ultrafast demagnetization in ferromagnets caused by femtosecond laser pulses, identifying temperature and chemical potential equilibration as the key driving forces, using a spin-resolved Boltzmann framework.

Contribution

It introduces a spin-resolved Boltzmann equation model incorporating Elliott-Yafet spin-flip scattering to analyze ultrafast magnetization dynamics.

Findings

Identifies temperature and chemical potential equilibration as the driving forces.

Predicts maximum magnetization quenching in nickel.

Provides a framework applicable to various ferromagnetic materials.

Abstract

Irradiating a ferromagnetic material with an ultrashort laser pulse leads to demagnetization on a femtosecond timescale. We implement Elliott-Yafet type spin-flip scattering, mediated by electron-electron and electron-phonon collisions, into the framework of a spin-resolved Boltzmann equation. Considering three mutually coupled reservoirs, (i) spin-up electrons, (ii) spin-down electrons and (iii) phonons, we trace non-equilibrium electron distributions during and after laser excitation. We identify the driving force for ultrafast magnetization dynamics as the equilibration of temperatures and chemical potentials between the electronic subsystems. This principle can be used to easily predict the maximum quenching of magnetization upon ultrashort laser irradiation in any material, as we show for the example of 3d-ferromagnetic nickel.