Ultrafast spin current generated by electron-magnon scattering in bulk of ferromagnets

Im Hyuk Shin, Byoung Chul Min, Byeong Kwon Ju, Gyung Min Choi

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12 Citations (Scopus)

Abstract

The ultrafast demagnetization of metallic ferromagnets can generate a spin current in metallic nonmagnets in a ferromagnet/nonmagnet structure. Two different mechanisms for this phenomenon have been suggested: spin-dependent transport of hot electrons and spin generation by electron-magnon scattering. In this work, we optically measure a transient spin accumulation on a nonmagnetic Cu layer driven by the ultrafast demagnetization of a ferromagnet (Fe, Co, and Ni). The modeling based on the spin generation by electron-magnon scattering in bulk ferromagnets (namely, bulk spin pumping) well explains the dynamics and magnitude of the measured spin accumulation on Cu.

Original languageEnglish
Article number090307
JournalJapanese journal of applied physics
Volume57
Issue number9
DOIs
Publication statusPublished - 2018 Sept

Bibliographical note

Funding Information:
In summary, we observe that the ultrafast demagnetization of a ferromagnet of Fe, Co, or Ni induces intense and ultrafast spin accumulation on a nonmagnet of Cu. The dynamics and magnitudes of the spin accumulation are well explained using the model based on the spin generation driven by heat transfer between electrons and magnons of ferromagnets. Our explanation differs from the spin Seebeck effect in that our model considers the electron–magnon scattering inside the bulk of ferromagnetic metals, and it can be named as “bulk spin pumping”. Analyzing the spin accumulation results with the bulk spin pumping leads to the determination of the spin relaxation time of ferromagnets. In particular, the spin relaxation time of Fe obtained by our analysis is shown to agree with the spin diffusion length obtained by electrical measurement under a steady-state condition. However, results of the spin relaxation times of Co and Ni do not agree with those of the electrical measurement. Possibly, other thermal mechanisms of the spin-dependent Seebeck effect and interfacial spin pumping might be involved. In addition, nonthermal mechanisms of the superdiffusive current and nonthermal spin pumping can contribute to measurements. Acknowledgment This work was supported by the National Research Council of Science and Technology (NST) Grant No. CAP-16-01-KIST by the Korea government (Ministry of Science and ICT) and the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2018R1C1B5041975).

Funding Information:
This work was supported by the National Research Council of Science and Technology (NST) Grant No. CAP-16-01-KIST by the Korea government (Ministry of Science and ICT) and the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2018R1C1B5041975).

Publisher Copyright:
© 2018 The Japan Society of Applied Physics.

ASJC Scopus subject areas

  • General Engineering
  • General Physics and Astronomy

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