Ultrafast magnetization dynamics in half-metallic Co${}_2$FeAl Heusler alloy

Abstract

We report on optically induced, ultrafast magnetization dynamics in the Heusler alloy $\mathrm{C}{\mathrm{o}}_2\mathrm{FeAl}$, probed by time-resolved magneto-optical Kerr effect. Experimental results are compared to results from electronic structure theory and atomistic spin-dynamics simulations. Experimentally, we find that the demagnetization time ($\ddot{I}{„}_M$) in films of $\mathrm{C}{\mathrm{o}}_2\mathrm{FeAl}$ is almost independent of varying structural order, and that it is similar to that in elemental 3d ferromagnets. In contrast, the slower process of magnetization recovery, specified by $\ddot{I}{„}_R$, is found to occur on picosecond time scales, and is demonstrated to correlate strongly with the Gilbert damping parameter ($\hat{I}\pm$). Our results show that $\mathrm{C}{\mathrm{o}}_2\mathrm{FeAl}$ is unique, in that it is the first material that clearly demonstrates the importance of the damping parameter in the remagnetization process. Based on these results we argue that for $\mathrm{C}{\mathrm{o}}_2\mathrm{FeAl}$ the remagnetization process is dominated by magnon dynamics, something which might have general applicability.