Role of electron and phonon temperatures in the helicity-independent all-optical switching of GdFeCo

TLDR

Ultrafast optical heating of electrons in ferrimagnetic metals can trigger all‑optical switching of magnetization. The study aims to quantify the temperature rise in GdFeCo thin films during helicity‑independent all‑optical switching. The authors performed quantitative measurements of electron and phonon temperature dynamics in GdFeCo thin films during helicity‑independent AOS. Critical switching fluences vary with initial sample temperature and pulse duration (55 fs–15 ps); non‑equilibrium phenomena are required for helicity‑independent AOS, yet peak electron temperature is not critical, and switching time increases with pulse duration, reaching ~13 ps for 10 ps pulses, raising questions about the fundamental mechanism.

Abstract

Ultrafast optical heating of the electrons in ferrimagnetic metals can result in all-optical switching (AOS) of the magnetization. Here we report quantitative measurements of the temperature rise of GdFeCo thin films during helicity-independent AOS. Critical switching fluences are obtained as a function of the initial temperature of the sample and for laser pulse durations from 55 fs to 15 ps. We conclude that non-equilibrium phenomena are necessary for helicity-independent AOS, although the peak electron temperature does not play a critical role. Pump-probe time-resolved experiments show that the switching time increases as the pulse duration increases, with 10 ps pulses resulting in switching times of ~sim 13 ps. These results raise new questions about the fundamental mechanism of helicity-independent AOS.