Anisotropic Laser-Pulse-Induced Magnetization Dynamics in van der Waals Magnet Fe$_3$GeTe$_2$

TL;DR

This study explores the ultrafast magnetization dynamics of Fe$_3$GeTe$_2$, revealing a two-step demagnetization process, temperature-dependent spin-relaxation, and the potential for external spin control, advancing 2D spintronics.

Contribution

It provides the first detailed microscopic analysis of femtosecond laser-induced magnetization dynamics in Fe$_3$GeTe$_2$, highlighting spin-flip probabilities and weak interlayer exchange.

Findings

Demonstrated a slow two-step demagnetization process.

Extracted spin-relaxation timescales as functions of temperature, field, and fluence.

Identified large spin-flip probability linked to strong spin-orbit coupling.

Abstract

Femtosecond laser-pulse excitation provides an energy efficient and fast way to control magnetization at the nanoscale, providing great potential for ultrafast next-generation data manipulation and nonvolatile storage devices. Ferromagnetic van der Waals materials have garnered much attention over the past few years due to their low dimensionality, excellent magnetic properties, and large response to external stimuli. Nonetheless, their behaviour upon fs laser-pulse excitation remains largely unexplored. Here, we investigate the ultrafast magnetization dynamics of a thin flake of Fe$_3$GeTe$_2$ (FGT) and extract its intrinsic magnetic properties using a microscopic framework. We find that our data is well described by our modelling, with FGT undergoing a slow two-step demagnetization, and we experimentally extract the spin-relaxation timescale as a function of temperature, magnetic field and excitation fluence. Our observations indicate a large spin-flip probability in agreement with a theoretically expected large spin-orbit coupling, as well as a weak interlayer exchange coupling. The spin-flip probability is found to increase when the magnetization is pulled away from its quantization axis, opening doors to an external control over the spins in this material. Our results provide a deeper understanding of the dynamics van der Waals materials upon fs laser-pulse excitation, paving the way towards two-dimensional materials-based ultrafast spintronics.