Element-selective tracking ultrafast demagnetization process in Co/Pt multilayer thin films by the resonant magneto-optical Kerr effect

TL;DR

This study uses resonant magneto-optical Kerr effect measurements with an x-ray free electron laser to reveal element-specific ultrafast demagnetization times in Co/Pt multilayer thin films, showing distinct dynamics for Co and Pt.

Contribution

It demonstrates element-specific ultrafast demagnetization times in Co/Pt films using resonant magneto-optical techniques at different elemental edges, highlighting the role of induced Pt moments.

Findings

Co demagnetization time: 80±60 fs

Pt demagnetization time: 640±140 fs

Element dependence explained by induced Pt moments

Abstract

We examined the photo-induced dynamics of ferromagnetic Co/Pt thin films demonstrating perpendicular magnetic anisotropy with element specificity using resonant polar magneto-optical Kerr effect measurements at Pt~N${}_{6,7}$ and Co~M${}_{2,3}$ edges with an x-ray free electron laser. The obtained results showed a clear element dependence of photo-induced demagnetization time scales: $\tau_\textrm{demag.}^\textrm{Co}=80\pm60~\textrm{fs}$ and $\tau_\textrm{demag.}^\textrm{Pt}=640\pm140~\textrm{fs}$. This dependence is explained by the induced moment of the Pt atom by current flow from the Co layer through the interfaces. The observed magnetization dynamics of Co and Pt can be attributed to the characteristics of photo-induced Co/Pt thin film phenomena including all-optical switching.