State-resolved ultrafast charge and spin dynamics in [Co/Pd] multilayers

TL;DR

This study employs circularly polarized x-ray spectroscopy to visualize ultrafast demagnetization in Co/Pd multilayers, revealing distinct dynamics of hole states below and above the Fermi level and elucidating the process involving spin-flip scattering and spin wave formation.

Contribution

It provides the first direct visualization of the different ultrafast demagnetization dynamics of hole states below and above the Fermi level in ferromagnetic multilayers.

Findings

Below Fermi level, demagnetization is instantaneous and strong.

Above Fermi level, demagnetization is delayed by approximately 35 fs.

Demonstrates the role of spin-flip scattering and spin waves in ultrafast demagnetization.

Abstract

We use transient absorption spectroscopy with circularly polarized x-rays to detect laser-excited hole states below the Fermi level and compare their dynamics with that of unoccupied states above the Fermi level in ferromagnetic [Co/Pd] multilayers. While below the Fermi level an instantaneous and significantly stronger demagnetization is observed, above the Fermi level the demagnetization is delayed by 35+/-10 fs. This provides a direct visualization of how ultrafast demagnetization proceeds via initial spin-flip scattering of laser-excited holes to the subsequent formation of spin waves.