Spatially resolved investigation of magnetization fluctuations in magnetic thin films

Abstract

Combining wide-field magneto-optical Kerr microscopy with a time series analysis scheme allows for investigating magnetization fluctuations with high spatial and temporal resolution. We use this technique to study magnetization fluctuations in a thin ferromagnetic film prepared in a quasi-equilibrium magnetic state via a demagnetization protocol. Our experiments reveal a spatially inhomogeneous noise response, with strongly localized fluctuation hot spots near magnetic domain walls scattered across the sample surface. The spatial density of the noise hot spots is very similar at different low magnetic field strengths, as expected from the fluctuation–dissipation theorem. The measurement scheme thus opens the way for the spatially resolved investigation of quasi-equilibrium noise processes in magnetic materials.