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Magnon spectrum of the amorphous ferromagnet Co4P from atomistic spin dynamics

Mai Kameda1,2, Gerrit E. W. Bauer1,3,4,5, and Joseph Barker1,6,7,*

  • 1Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
  • 2Department of Applied Physics, Nagoya University, Nagoya 464-8603, Japan
  • 3WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
  • 4Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
  • 5Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
  • 6School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, United Kingdom
  • 7Bragg Centre for Materials Research, University of Leeds, Leeds LS2 9JT, United Kingdom

  • *Corresponding author: j.barker@leeds.ac.uk
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Phys. Rev. B 106, L060403 – Published 11 August, 2022

DOI: https://doi.org/10.1103/PhysRevB.106.L060403

Abstract

The gapped local minimum in the magnon dispersion, located at a finite wave number and frequency, has been observed in the amorphous ferromagnet Co4P. The feature is called a “rotonlike” excitation and has eluded explanation for decades. We overcome the limitations of previous theories by combining the reverse Monte Carlo method, to determine the atomic structure, with large-scale atomistic spin simulations. This method enables us to include atomic order and spin correlations on an equal footing. We find the rotonlike feature is actually gapless, in contrast to the gapped structure found in previous studies. The gapless feature is attributed to amorphous umklapp scattering caused by residual structural order.

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Phys. Rev. B 106, L060403– Published 11 August, 2022
  • Received 18 January 2022
  • Revised 3 April 2022
  • Accepted 26 July 2022
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