Realistic micromagnetic description of all-optical ultrafast switching processes in ferrimagnetic alloys

TL;DR

This paper develops a micromagnetic model based on the extended Landau-Lifshitz-Bloch equation to accurately simulate all-optical ultrafast switching in ferrimagnetic alloys, bridging the gap between atomistic simulations and real-world experiments.

Contribution

The authors introduce a robust micromagnetic framework validated against atomistic results, enabling realistic large-scale simulations of all-optical switching in ferrimagnets.

Findings

Helicity-independent switching is a thermal process linked to electron temperature.

Size of inverted magnetic area correlates with maximum electron temperature.

Differences between magnetic circular dichroism and inverse Faraday effect predictions are highlighted.

Abstract

Both helicity-independent and helicity-dependent all-optical switching processes driven by single ultrashort laser pulse have been experimentally demonstrated in ferrimagnetic alloys as GdFeCo. Although the switching has been previously reproduced by atomistic simulations, the lack of a robust micromagnetic framework for ferrimagnets limits the predictions to small nano-systems, whereas the experiments are usually performed with lasers and samples of tens of micrometers. Here we develop a micromagnetic model based on the extended Landau-Lifshitz-Bloch equation, which is firstly validated by directly reproducing atomistic results for small samples and uniform laser heating. After that, the model is used to study ultrafast single shot all-optical switching in ferrimagnetic alloys under realistic conditions. We find that the helicity-independent switching under a linearly polarized laser pulse is a pure thermal phenomenon, in which the size of inverted area directly correlates with the maximum electron temperature in the sample. On the other hand, the analysis of the helicity-dependent processes under circular polarized pulses in ferrimagnetic alloys with different composition indicates qualitative differences between the results predicted by the magnetic circular dichroism and the ones from inverse Faraday effect. Based on these predictions, we propose experiments that would allow to resolve the controversy over the physical phenomenon that underlies these helicity-dependent all optical processes.