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 multicomponent magnetic alloys and compounds, the speed of demagnetization and spin switching processes has an element‐specific character, the magnetization damping was assumed to be a universal parameter for all constituent magnetic elements irrespective of their different spin–orbit couplings and electronic structure. Herein, experimental and theoretical evidence for an element‐specific magnetic damping parameter is provided by investigating the ultrafast magnetization response of a high‐anisotropy ferrimagnetic DyCo5 alloy to femtosecond laser excitation. Strikingly different demagnetization and remagnetization dynamics of Dy and Co magnetic moments is revealed by employing femtosecond laser pump–X‐ray magnetic circular dichroism probe measurements combined with atomistic spin dynamics (ASD) simulations using ab initio calculated parameters. 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. These findings can be used as a recipe for tuning the speed and magnitude of laser‐driven magnetic processes and consequently allow control over various dynamic functionalities in multicomponent magnetic materials.
Highlights
Manipulation and control of magnetism by light is one of the key concepts of modern research in magnetism with direct and far-reaching implications for magnetic data recording.[1,2] Of particular interest for both fundamental and applied science is the use of femtosecond laser pulses to fully control the orientation of a spin ensemble on ultrashort timescales
This ultrafast spin switching process was mediated by an unexpected transient ferromagnetic-like state (TFLS), which has been identified as the driving microscopic mechanism behind thermally induced switching in ferrimagnetic alloys.[3]
The stoichiometry of the ferrimagnetic alloy was controlled by varying the deposition rate of separate chemical elements during cosputtering
Summary
Manipulation and control of magnetism by light is one of the key concepts of modern research in magnetism with direct and far-reaching implications for magnetic data recording.[1,2] Of particular interest for both fundamental and applied science is the use of femtosecond (fs) laser pulses to fully control the orientation of a spin ensemble on ultrashort timescales. A cornerstone in this respect was the discovery of thermally induced magnetization switching in ferrimagnetic GdFeCo via a single fs laser pulse excitation This ultrafast spin switching process was mediated by an unexpected transient ferromagnetic-like state (TFLS), which has been identified as the driving microscopic mechanism behind thermally induced switching in ferrimagnetic alloys.[3]. Radu Fachbereich Physik Freie Universität Berlin Arnimallee 14, Berlin 14195, Germany. The experimental observations reveal distinctly different demagnetization times and remagnetization behaviors for Dy and Co. To understand the time evolution of these processes, we use atomistic spin dynamics (ASD) simulations using an ab initio calculated spin Hamiltonian.[11] Simulation results and the X-ray magnetic circular dichroism (XMCD) measurements are compared in a quantitative manner to determine the distinct, element-specific damping coefficients of Dy and Co spins. These findings provide the first direct experimental and theoretical evidence for an element-specific damping in ferrimagnetic alloys
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