Distinguishing Local and non-Local Demagnetization in Ferromagnetic FePt Nanoparticles

Patrick W. Granitzka; Alexander H. Reid; Jerome Hurst; Emmanuelle Jal; Loïc Le Guyader; Tian-Min Liu; Leandro Salemi; Daniel J. Higley; Tyler Chase; Zhao Chen; Marco Berritta; William F. Schlotter; Hendrik Ohldag; Georgi L. Dakovski; Sebastian Carron; Matthias C. Hoffmann; Jian Wang; Virat Mehta; Olav Hellwig; Eric E. Fullerton; Yukiko K. Takahashi; Joachim Stöhr; Peter M. Oppeneer; Hermann A. Dürr

arXiv · 1903.08287

Distinguishing Local and non-Local Demagnetization in Ferromagnetic FePt Nanoparticles

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Abstract

Time-resolved coherent X-ray diffraction is used to measure the spatially resolved magnetization structure within FePt nanoparticles during laser-induced ultrafast demagnetization. The momentum-dependent X-ray magnetic diffraction shows that demagnetization proceeds at different rates at different X-ray momentum transfer. We show that the observed momentum-dependent scattering has the signature of inhomogeneous demagnetization within the nanoparticles, with the demagnetization proceeding more rapidly at the boundary of the nanoparticle. A shell region of reduced magnetization forms and moves inwards at a supermagnonic velocity. Spin-transport calculations show that the shell formation is driven by superdiffusive spin flux mainly leaving the nanoparticle into the surrounding carbon. Quantifying this non-local contribution to the demagnetization allows us to separate it from the local demagnetization.

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Patrick W. Granitzka, Alexander H. Reid, Jerome Hurst, Emmanuelle Jal, Loïc Le Guyader, Tian-Min Liu, Leandro Salemi, Daniel J. Higley, Tyler Chase, Zhao Chen, Marco Berritta, William F. Schlotter, Hendrik Ohldag, Georgi L. Dakovski, Sebastian Carron, Matthias C. Hoffmann, Jian Wang, Virat Mehta, Olav Hellwig, Eric E. Fullerton, Yukiko K. Takahashi, Joachim Stöhr, Peter M. Oppeneer, Hermann A. Dürr. 2019-03-19. Distinguishing Local and non-Local Demagnetization in Ferromagnetic FePt Nanoparticles. https://arxiv.org/abs/1903.08287

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