Studying all-optical magnetization switching of GdFe by double-pulse laser excitation

TL;DR

This study investigates the ultrafast all-optical magnetization switching in GdFe using double-pulse laser excitation, revealing how pulse timing and fluence influence the switching process and demonstrating the potential for high-speed data writing.

Contribution

It provides new insights into the timing and fluence conditions for all-optical switching in GdFe, supported by experimental data and atomistic spin dynamics simulations.

Findings

Reswitching occurs with a 3 ps delay and specific fluence ratios.

Switching persists up to 40 ps delay, limited by cooling and remagnetization time.

Pulse addition effect enables sub-threshold switching for shorter delays.

Abstract

The tremendous interest in the technology and underlying physics of all-optical switching of magnetization brings up the question of how fast the switching can occur and how high the frequency of writing the data with ultrafast laser pulses can be. To answer this question, we excited a GdFe ferrimagnetic alloy, the magnetization of which can be reversed by single laser pulses, a phenomenon known as toggle switching, by two pulses with a certain time delay in between. Using photoemission electron microscopy and Kerr microscopy for magnetic domain imaging, we explore the effects of varying fluences of the first and second pulse as well as the time delay between the two pulses. Our results show that when the fluence of the first pulse is adjusted just above the threshold of single-pulse switching, a second pulse with about 60% of the fluence of the first pulse, arriving only 3 ps later, switches the magnetization back. This reswitching persists up to about 40 ps pulse separation. We interpret the latter as the time required for the sample to cool down and remagnetize after the first pulse. For shorter time delays below about 2 ps, no re-switching occurs. However, the effect of the two pulses adds up, enabling switching for fluences of both pulses below the threshold for single-pulse switching. Atomistic spin dynamics simulations are used to model the experimental data, successfully confirming our results.