Tracing the thermal mechanism in femtosecond spin dynamics

TL;DR

This paper investigates the ultrafast thermal processes responsible for demagnetization in nickel using femtosecond experiments and micromagnetic modeling, highlighting the role of thermal mechanisms and fluence-dependent rates.

Contribution

It demonstrates that thermal effects dominate femtosecond spin dynamics in Ni and introduces a coupled model to explain the fluence-dependent relaxation times.

Findings

Demagnetization and recovery rates increase with laser fluence.

Slowing of dynamics at high fluences is due to increased relaxation times.

Thermal mechanisms are the primary drivers of ultrafast spin changes.

Abstract

We compare femtosecond pump-probe experiments in Ni and micromagnetic modelling based on the Landau-Lifshitz-Bloch equation coupled to a two-temperature model, revealing a predominant thermal ultrafast demagnetization mechanism. We show that both spin (femtosecond demagnetization) and electron-phonon (magnetization recovery) rates in Ni increase as a function of the laser pump fluence. The slowing down for high fluences arises from the increased longitudinal relaxation time.