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

Abstract

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, $S(\nu )$, exhibits a remarkably robust ${\nu }^{-3/2}$ power law over frequencies $\nu$ from 1~kHz to 1~MHz. As the SRT region is traversed, however, $S(\nu )$ spectra develop a steadily-increasing critical frequency, ${\nu }_0$, 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.

References in corpus (16)

• Dynamics of Dzyaloshinskii domain walls in ultrathin magnetic films
• Asymmetric Magnetic Domain-Wall Motion by the Dzyaloshinskii-Moriya Interaction
• Spectroscopy of spontaneous spin noise as a probe of spin dynamics and magnetic resonance
• Spin noise spectroscopy in GaAs
• Noise in disordered systems: The power spectrum and dynamic exponents in avalanche models
• Spin noise of electrons and holes in self-assembled quantum dots
• Dynamics of a ferromagnetic domain wall and the Barkhausen effect
• Domain structure in CoFeB thin films with perpendicular magnetic anisotropy
• Optical measurements of spin noise as a high resolution spectroscopic tool
• Self similar Barkhausen noise in magnetic domain wall motion
• Giant modulation of the magnetic domain size induced by an electric field
• Tracking random walk of individual domain walls in cylindrical nanomagnets with resistance noise
• Higher Order Spin Noise Statistics
• Statistical properties of Barkhausen noise in amorphous ferromagnetic films
• Nonequilibrium Spin Noise and Noise of Susceptibility
• Monitoring superparamagnetic Langevin behavior of individual $\mathrm{SrRu}{\mathrm{O}}_3$ nanostructures

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