Broadband optical spectroscopy of stochastic ferromagnetic fluctuations across a spin-reorientation transition

ORAL

Abstract

We use the magneto-optical Kerr effect to measure frequency spectra of stochastic magnetic fluctuations between 1 kHz and 1 MHz in a Pt/Co/Pt trilayer with anisotropy that has been laterally graded through a spin-reorientation transition. On regions of the film with strong perpendicular anisotropy, the fluctuation power obeys a power law over three orders of magnitude in frequency. Fluctuation spectra measured in regions with weaker anisotropy show a cutoff frequency below which the spectra are approximately frequency independent. We identify this cutoff as characterizing the maximum lifetime of ferromagnetic states, and find that it is sensitive to magnetic anisotropy, temperature, and applied magnetic field. Finally, the fluctuations show higher-order correlations which reveal temporal symmetry breaking, appearing upon application of magnetic field. These measurements establish magnetization fluctuation spectroscopy as a sensitive tool for characterizing ferromagnetic behavior and phase transitions.

*We gratefully acknowledge the support of the U.S. Department of Energy through the LANL LDRD Program.

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Presenters

  • Andrew Balk

    • National High Magnetic Field Laboratory, Los Alamos National Laboratory
    • National High Magnetic Field Laboratory, Los Alamos National Lab

Authors

  • Andrew Balk

    • National High Magnetic Field Laboratory, Los Alamos National Laboratory
    • National High Magnetic Field Laboratory, Los Alamos National Lab

  • Fuxiang Li

    • Center for Nonlinear Studies, Los Alamos National Laboratory
    • Center for Nonlinear Studies and Theoretical Division, Los Alamos National Laboratory

  • Ian Gilbert

    • Center for Nanoscale Science and Technology, National Institute of Standards and Technology

  • John Unguris

    • Center for Nanoscale Science and Technology, National Institute of Standards and Technology

  • Nikolai Sinitsyn

    • Theoretical Division, Los Alamos National Laborary
    • Los Alamos National Laboratory
    • Theoretical Division, Los Alamos National Laboratory
    • Theoretical Division, Los Alamos National Lab

  • Scott Crooker

    • National High Magnetic Field Laboratory, Los Alamos National Laboratory
    • National High Magnetic Field Laboratory, Los Alamos National Lab
    • Los Alamos National Laboratory
    • NHMFL, Los Alamos National Laboratory