Ultrafast demagnetization of Pt magnetic moment in L10-FePt probed by magnetic circular dichroism at a hard x-ray free electron laser

Kohei Yamamoto, Yuya Kubota, Motohiro Suzuki, Yasuyuki Hirata, Karel Carva, Marco Berritta, Kou Takubo, Yohei Uemura, Ryo Fukaya, Kenta Tanaka, Wataru Nishimura, Takuo Ohkochi, Tetsuo Katayama, Tadashi Togashi, Kenji Tamasaku, Makina Yabashi, Yoshihito Tanaka, Takeshi Seki, Koki Takanashi, Peter M. OppeneerHiroki Wadati

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


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 τpt = 0.61 ± 0.04 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 τtotal < 0.1. 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.

Original languageEnglish
Article number123010
JournalNew Journal of Physics
Issue number12
Publication statusPublished - 2019 Dec 12


  • XFEL
  • photo-induced magnetization dynamics
  • time-resolved XMCD

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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