Electron-phonon interaction during optically induced ultrafast magnetization dynamics of Au/GdFeCo bilayers

TL;DR

This study investigates the electron-phonon coupling during ultrafast magnetization dynamics in Au/GdFeCo bilayers by analyzing thermal transport and reflectance changes, revealing a coupling constant of 6 x 10^17 W/(m^3-K).

Contribution

It introduces a method to accurately determine electron-phonon coupling in magnetic metals using bilayer thermal modeling and reflectance analysis, accounting for magnetization effects.

Findings

Electron-phonon coupling constant in GdFeCo is 6 x 10^17 W/(m^3-K).

Electron-phonon relaxation time in GdFeCo is approximately 150 fs.

Reflectance of Au layer effectively monitors phonon temperature during optical heating.

Abstract

The temperature evolution of GdFeCo electrons following optical heating plays a key role in all optical switching of GdFeCo and is primarily governed by the strength of coupling between electrons and phonons. Typically, the strength of electron-phonon coupling in a metal is deduced by monitoring changes in reflectance following optical heating and then analyzing the transient reflectance with a simple two-temperature thermal model. In a magnetic metal, the change in reflectance cannot be assumed to depend only the electron and phonon temperatures because a metal's reflectance also depends on the magnetization. To deduce the electron-phonon coupling constant in GdFeCo, we analyze thermal transport in Au and GdFeCo bilayers following optical heating of the GdFeCo electrons. We use the reflectance of the Au layer to monitor the temperature evolution of the Au phonons. By interpreting the response of the bilayer to heating with a thermal model, we determine the electron-phonon coupling constant in GdFeCo to be 6 x 10^17 W/(m^3-K) corresponding to an electron-phonon relaxation time in GdFeCo of ~150 fs.