Abstract
Unraveling the origin of ultrafast demagnetization in multisublattice ferromagnetic materials requires femtosecond x-ray techniques to trace the magnetic moment dynamics on individual elements, but this could not yet be achieved in the hard x-ray regime. We demonstrate here the first ultrafast demagnetization dynamics in the ferromagnetic heavy 5d-transition metal Pt using circularly-polarized hard x-rays at an x-ray free electron laser (XFEL). The decay time of laser-induced demagnetization of L10-FePt is determined to be using time-resolved x-ray magnetic circular dichroism at the Pt L3 edge, whereas magneto-optical Kerr measurements indicate the decay time for the total magnetization as . A transient magnetic state with a photo-modulated ratio of the 3d and 5d magnetic moments is demonstrated for pump–probe delays larger than 1 ps. We explain this distinct photo-modulated transient magnetic state by the induced-moment behavior of the Pt atom and the x-ray probing depth. Our findings pave the way for the future use of XFELs to disentangle atomic spin dynamics contributions.
Highlights
We report the first hard x-ray time-resolved x-ray magnetic circular dichroism (trXMCD) measurements of the spin dynamics of the Pt moment in FePt using the x-ray free electron laser (XFEL) with an x-ray phase retarder to produce circular polarized x-rays [27]. x-ray phase retarders have been widely used in several synchrotron radiation facilities such as the advanced photon source [28], European Synchrotron Radiation Facility [29, 30] and SPring-8 [31]
We have studied the Pt magnetization dynamics in L10-FePt thin films with trXMCD using ultrashort and circularly polarized XFEL pulses at the Pt L edge in the hard x-ray regime
With the complementary use of time-resolved magneto-optical Kerr effect (trMOKE) measurements we demonstrated an element-specific demagnetization process with different decay times of
Summary
Original content from this 2 Department of Physics, University of Tokyo, Hongo, Tokyo 113-0033, Japan work may be used under 3 Institute for Molecular Science, Okazaki, Aichi 444-8585, Japan the terms of the Creative 4 Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo, Hyogo 679-5198, Japan. 11 Center for Spintronics Research Network, Tohoku University, Sendai, Miyagi 980-8577, Japan
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