Ferromagnetic Resonance Linewidth and Internal Biasing Field in Ni-Fe Films as a Function of Dispersion in the Anisotropy Field Magnitude

Abstract

Ferromagnetic resonance techniques have been used to measure the magnetic properties of Ni‐Fe films in the 50–1500 Mc/sec range. Resonance was observed in the plane of films 8 mm in diameter and 600–2600 Å thick. The primary purpose of the investigation was to obtain a correlation between the resonance linewidth extrapolated to zero frequency (ΔH)₀, and the dispersion in anisotropy field magnitude Δ₉₀. The zero‐frequency linewidths found were about 2.8 times the values calculated theoretically from values of anisotropy field magnitude dispersion independently obtained in this laboratory. Plots of the resonance frequency squared as a function of resonance field showed a shift, or internal bias H_i, toward positive field values as others have observed. There was little or no shift for films with Δ₉₀ less than about 0.2, but for larger dispersion, the shift increased approximately linearly with Δ₉₀. A very good linear correlation was found between H_i and α₀, the high‐frequency damping parameter. It is suggested that the internal biasing field may be associated with the magnetization rippling that Fuller and Hale and Feldtkeller have observed in electron micrographs. Also, it may be possible that the larger‐than‐expected values of (ΔH)₀, and the wide variation in α₀ values (0.006–0.03) reported here are caused by the energy loss, which Feldtkeller has termed ``ripple hysteresis,'' associated with the movement of the small‐angle walls, which result from the magnetization rippling.