[EN]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 nanosystems, 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 one to resolve the controversy over
the physical phenomenon that underlies these helicity-dependent all optical processes.
