Element-selective probing of ultrafast ferromagnetic--antiferromagnetic order dynamics in Fe/CoO bilayers

TL;DR

This study investigates the ultrafast element-specific magnetic order dynamics in Fe/CoO bilayers using resonant soft-x-ray reflectivity, revealing rapid demagnetization within 300 fs driven mainly by energy transfer from Fe electrons to CoO.

Contribution

It provides the first element-resolved measurements of ultrafast magnetic order loss in Fe/CoO bilayers and identifies the dominant demagnetization mechanism via atomistic spin simulations.

Findings

Both CoO and Fe lose magnetic order within 300 fs.

Energy transfer from Fe electrons to CoO drives demagnetization.

Ultrafast dynamics are captured with 120 fs resolution.

Abstract

The ultrafast magnetization dynamics of an epitaxial Fe/CoO bilayer on Ag(001) is examined in an element-resolved way by resonant soft-x-ray reflectivity. The transient magnetic linear dichroism at the Co L2 edge and the magnetic circular dichroism at the Fe L3 edge measured in reflection in a pump-probe experiment with 120 fs temporal resolution show the loss of antiferromagnetic and ferromagnetic order in CoO and Fe, respectively, both within 300 fs after excitation with 60 fs light pulses of 800 and 400 nm wavelengths. Comparison to spin-dynamics simulations using an atomistic spin model shows that direct energy transfer from the laser-excited electrons in Fe to the magnetic moments in CoO provides the dominant demagnetization channel in the case of 800-nm excitation.