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Title: Broadband Spectroscopy of Thermodynamic Magnetization Fluctuations through a Ferromagnetic Spin-Reorientation Transition

Journal Article · · Physical Review. X
 [1];  [1];  [2];  [2];  [1];  [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Center for Nanoscale Science and Technology

We use scanning optical magnetometry to study the broadband frequency spectra of spontaneous magnetization fluctuations, or “magnetization noise,” in an archetypal ferromagnetic film that can be smoothly tuned through a spin-reorientation transition (SRT). The SRT is achieved by laterally varying the magnetic anisotropy across an ultrathin Pt / Co / Pt trilayer, from the perpendicular to in-plane direction, via graded Ar + irradiation. In regions exhibiting perpendicular anisotropy, the power spectrum of the magnetization noise S(ν) exhibits a remarkably robust ν - 3 / 2 power law over frequencies ν from 1 kHz to 1 MHz. As the SRT region is traversed, however, S(ν) spectra develop a steadily increasing critical frequency ν 0 , below which the noise power is spectrally flat, indicating an evolving low-frequency cutoff for magnetization fluctuations. The magnetization noise depends strongly on applied in- and out-of-plane magnetic fields, revealing local anisotropies and also a field-induced emergence of fluctuations in otherwise stable ferromagnetic films. Finally, we demonstrate that higher-order correlators can be computed from the noise. These results highlight broadband spectroscopy of thermodynamic fluctuations as a powerful tool to characterize the interplay between thermal and magnetic energy scales, and as a means of characterizing phase transitions in ferromagnets.

Research Organization:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE; LANL Laboratory Directed Research and Development (LDRD) Program; National Science Foundation (NSF)
Grant/Contract Number:
AC52-06NA25396; DMR-1157490
OSTI ID:
1471805
Alternate ID(s):
OSTI ID: 1479988
Report Number(s):
LA-UR-18-22421
Journal Information:
Physical Review. X, Vol. 8, Issue 3; ISSN 2160-3308
Publisher:
American Physical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 12 works
Citation information provided by
Web of Science

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Cited By (3)

Detection and amplification of spin noise using scattered laser light in a quantum-dot microcavity journal January 2020
Bubble Magnetometry of Nanoparticle Heterogeneity and Interaction journal June 2019
Detection and amplification of spin noise using scattered laser light in a quantum-dot microcavity text January 2019

Figures / Tables (7)