Transient Exchange Interaction in a Helical Antiferromagnet

TL;DR

This study investigates the dynamic response of helical magnetic order in Dy to spin injection, revealing slower spin dynamics influenced by temperature and excitation fluence, linked to changes in the conduction electron Fermi surface.

Contribution

It provides the first time-resolved analysis of exchange interactions in a helical antiferromagnet, highlighting the role of conduction electron Fermi surface changes.

Findings

Spin dynamics are slower in helical order than in ferromagnetic phases.

Spin response depends strongly on temperature and excitation fluence.

Transient Fermi surface changes mediate the transfer of excitation to core spins.

Abstract

We have performed time-resolved resonant x-ray scattering studies in the Lanthanide metal Dy to reveal the dynamic response of the helical order exchange coupling to injection of unpolarized spins. The observed spin dynamics are significantly slower than that exhibited by the ferromagnetic phase in Lanthanide metals and are strongly dependent on temperature and excitation fluence. This unique behavior results from transient changes in the shape of the conduction electron Fermi surface and subsequent scattering events that transfer the excitation to the core spin.