Element‐specific Magnetization Damping in Ferrimagnetic DyCo₅ Alloys Revealed by Ultrafast X‐ray Measurements

Abstract

The dynamic response of magnetically‐ordered materials to an ultrashort external stimulus depends on microscopic parameters such as magnetic moment, exchange and spin‐orbit interactions. Whereas it is well established that, in multi‐component magnetic alloys and compounds, the speed of demagnetization and spin switching processes has an element‐specific character, the magnetization damping has been assumed to be a universal parameter for all constituent magnetic elements irrespective of their different spin‐orbit couplings and electronic structure. Here, we provide experimental and theoretical evidence for an element‐specific magnetic damping parameter by investigating the ultrafast magnetization response of a high‐anisotropy ferrimagnetic DyCo5 alloy to femtosecond laser excitation. Employing femtosecond laser pump – X‐ray magnetic circular dichroism (XMCD) probe measurements combined with atomistic spin dynamics (ASD) simulations using ab‐initio calculated parameters we reveal a strikingly different demagnetization and remagnetization dynamics of the Dy and Co magnetic moments upon photo‐excitation. These observations, fully corroborated by the ASD simulations, are linked to the element‐specific spin‐orbit coupling strengths of Dy and Co, which are incorporated in the phenomenological magnetization damping parameters. Our findings can be used as a recipe for tuning the speed and magnitude of laser‐driven magnetic processes and consequently allowing to control various dynamic functionalities in multi‐component magnetic materials.