Observations of ferromagnetic resonance modes on FeCo-based nanocrystalline alloys

Abstract

Uniform and symmetric resonance modes (known as Aharoni’s exchange resonance modes) are derived from micromagnetic equilibrium condition in the linear approximation. To investigate the uniform and symmetric resonance modes in ferromagnetic nanoscale grains, the microwave permeability of FeCo-based nanocrystalline alloy particles/paraffin composites was measured and calculated in the range 0.5–18 GHz. The measured dynamic permeability curves exhibit a broad resonance band at 4–6 GHz; some curves also exhibit a narrow resonance band at 13 GHz. The former behavior is in qualitative agreement with the uniform mode, and the latter is attributed to the first eigenvalue mode of the symmetric resonance modes excited in nanocrystalline monodomain grains in FeCo-based alloys. The difference value (Δ ω 11) between the uniform resonance frequency and the first frequency eigenvalue of the symmetric resonance modes shows good agreement with experiment.