Broadband spectroscopy of thermodynamic magnetization fluctuations through a ferromagnetic spin- reorientation transition

Published

September 21, 2018

Author(s)

a L. Balk, F Li, Ian J. Gilbert, John Unguris, N A. Sinitsyn, S A. Crooker

Abstract

We use scanning optical magnetometry to study the broadband frequency spectra of spontaneous magnetization fluctuations, or "magnetization noise", in an archetypal ferromagnetic 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(), exhibits a remarkably robust 􀀀3=2 power law over frequencies from 1 kHz - 1MHz. As the SRT region is traversed, however, S() spectra develop a steadily-increasing critical frequency, 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 fi eld-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.

Citation

Physical Review X

Volume

8

Issue

3

Pub Type

Journals

Download Paper

https://doi.org/10.1103/PhysRevX.8.031078

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Keywords

magnetization noise, spin reorientation, magnetic fluctuations

Citation

Balk, A. , Li, F. , Gilbert, I. , Unguris, J. , Sinitsyn, N. and Crooker, S. (2018), Broadband spectroscopy of thermodynamic magnetization fluctuations through a ferromagnetic spin- reorientation transition, Physical Review X, [online], https://doi.org/10.1103/PhysRevX.8.031078, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=925090 (Accessed October 13, 2025)