Femtosecond charge and spin dynamics in CoPt alloys

TL;DR

This study uses ultrafast X-ray techniques to observe femtosecond charge and spin dynamics in CoPt alloys, revealing rapid demagnetization linked to orbital hybridization and spin-orbit coupling differences.

Contribution

It demonstrates femtosecond-scale magnetic response in CoPt alloys using advanced X-ray free-electron laser techniques, highlighting the role of orbital hybridization.

Findings

Comparable demagnetization in CoPt and CoPd despite weaker excitation

Different orbital hybridization and spin-orbit coupling influence dynamics

Ultrafast X-ray methods effectively resolve femtosecond magnetic processes

Abstract

The use of advanced X-ray sources plays a key role in the study of dynamic processes in magnetically ordered materials. The progress in X-ray free electron lasers enables the direct and simultaneous observation of the femtosecond evolution of electron and spin systems through transient X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD), respectively. Such experiments allow us to resolve the response seen in the population of the spin-split valence states upon optical excitation. Here, we utilize circularly polarized ultrashort soft X-ray pulses from the new helical afterburner undulator at the free-electron laser FLASH in Hamburg to study the femtosecond dynamics of a laser-excited CoPt alloy at the Co $L_{3}$ absorption edge. Despite employing a weaker electronic excitation level we find a comparable demagnetization for the Co $3d$-states in CoPt compared to previous measurements on CoPd. This is attributed to distinctly different orbital hybridization and spin-orbit coupling between $3d$ and $4d$ vs. $3d$ and $5d$ elements in the corresponding alloys and multilayers.