Element specific ultrafast demagnetization was studied in Fe1−xNix alloys, covering the concentration range between 0.1<x<0.9. For all compositions, we observe a delay in the onset of Ni demagnetization relative to the Fe demagnetization. We find that the delay is correlated to the Curie temperature and hence also the exchange interaction. The temporal evolution of demagnetization is fitted to a magnon diffusion model based on the presupposition of enhanced ultrafast magnon generation in the Fe sublattice. The spin wave stiffness extracted from this model correspond well to known experimental values.
@article{arxiv.1810.11001,
title = {Exchange dependent ultrafast magnetization dynamics in Fe$_{1-x}$Ni$_{x}$ alloys},
author = {Somnath Jana and Ronny Knut and Erna K. Delczeg-Czirjak and Rameez S. Malik and Robert Stefanuik and Raghuveer Chimata and Dibya Phuyal and Venkata Mutta and Serkan Akansel and Daniel Primetzhofer and Martina Ahlberg and Johan Söderström and Johan Åkerman and Peter Svedlindh and Olle Eriksson and Olof Karis},
journal= {arXiv preprint arXiv:1810.11001},
year = {2018}
}