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Inhomogeneous magnon scattering during ultrafast demagnetization



Ronny J. Knut, Erna Delczeg-Czirjak, Somnath Jana, Justin M. Shaw, Hans T. Nembach, Yaroslav Kvashnin, Robert Stefaniuk, Rameez Malik, Patrik Grychtol, Dmitriy Zusin, Christian Gentry, Raghuveer Chimata, Manuel Pereiro, Johan Soderstrom, Emrah Turgut, Martina Ahlberg, Johan Akerman, H C. Kapteyn, Margaret M. Murnane, Dario A. Arena, Olle Eriksson, Olof Karis, Thomas J. Silva


Ni0.8Fe0.2 (Py) and Py alloyed with Cu exhibit intriguing ultrafast demagnetization behavior, where the Ni magnetic moment shows a delayed response relative to the Fe, an effect which is strongly enhanced by Cu alloying. We have studied a broad range of Cu concentrations to elucidate the effects of Cu alloying in Py. The orbital/spin magnetic moment ratios are largely unaffected by Cu alloying, signifying that Cu-induced changes in the ultrafast demagnetization are not related to spin-orbit interactions. We show that magnon diffusion can explain the delayed Ni response, which we attribute to an enhanced magnon generation rate in the Fe sublattice relative to the Ni sublattice. Furthermore, Py exhibits prominent RKKY-like exchange interactions, which are strongly enhanced between Fe atoms and diminished between Ni atoms by Cu alloying. An increased Fe magnon scattering rate is expected to occur concurrently with this increased Fe-Fe exchange interaction, supporting the results obtained from the magnon diffusion model.
Nature Physics


inhomogeneous, magnon scattering, ultrafast demagnetization, orbital, spin, interactions
Created October 25, 2018, Updated June 16, 2020