A comparative study of FMR and Brillouin light scattering on amorphous Fe40Ni40B20

It is shown that magnetic surface mode frequencies in the amorphous ferromagnet Fe₄₀Ni₄₀B₂₀ measured using Brillouin light scattering depend upon the incident laser light intensity: presumably due to local heating of the specimen due to the concentration of the light flux into a focal spot only a few microns in diameter. Surface mode frequencies extrapolated to zero light intensity are shown to be consistent with magnetic parameters measured using ferromagnetic resonance at 35.731 GHz to within ±0.5 GHz for specimens of amorphous Fe₄₀Ni₄₀B₂₀. 0.5 GHz corresponds to a change of 0.17 kG in the saturation magnetization, 4πM_s.