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.
@article{arxiv.1708.08918,
title = {Element-resolved ultrafast demagnetization rates in ferrimagnetic CoDy},
author = {T. Ferte and N. Bergeard and L. Le Guyader and M. Hehn and G. Malinowski and E. Terrier and E. Otero and K. Holldack and N. Pontius and C. Boeglin},
journal= {arXiv preprint arXiv:1708.08918},
year = {2017}
}