Element-resolved ultrafast demagnetization rates in ferrimagnetic CoDy

TL;DR

This study investigates element-specific ultrafast demagnetization in CoDy alloys, revealing distinct dynamics for Co and Dy sublattices and a temperature-dependent increase in Dy demagnetization rates.

Contribution

It provides the first element-resolved measurements of ultrafast demagnetization rates in CoDy alloys, highlighting a twofold increase in Dy rates at low temperature.

Findings

Dy demagnetization rates increase at low temperature

Co demagnetization rates remain constant across temperatures

Element-specific dynamics differ between Co and Dy

Abstract

Femtosecond laser induced ultrafast magnetization dynamics have been studied in multisublattice CoxDy1-x alloys. By performing element and time-resolved X-ray spectroscopy, we distinguish the ultrafast quenching of Co3d and Dy4f magnetic order when the initial temperatures are below (T=150K) or above (T=270K) the temperature of magnetic compensation (Tcomp). In accordance with former element-resolved investigations and theoretical calculations, we observe different dynamics for Co3d and Dy4f spins. In addition we observe that, for a given laser fluence, the demagnetization amplitudes and demagnetization times are not affected by the existence of a temperature of magnetic compensation. However, our experiment reveals a twofold increase of the ultrafast demagnetization rates for the Dy sublattice at low temperature. In parallel, we measure a constant demagnetization rate of the Co3d sublattice above and below Tcomp. This intriguing difference between the Dy4f and Co3d sublattices calls for further theoretical and experimental investigations.