Temperature Dependence of the Ferromagnetic Resonance Linewidth in Thin Ni–Fe Films

Abstract

Linewidths for ferromagnetic resonance with the static magnetic field in the film plane have been measured at frequencies from 1–9 Gc/sec and temperatures from 4.2°–300°K for Ni–Fe alloy films (77% Ni) 150 to 1500 Å thick. The linewidth exhibits a maximum in the vicinity of 80°K and the effect is generally larger in thinner films. The amplitude of the linewidth temperature dependence is independent of frequency and the maximum shifts to slightly higher temperatures with increasing frequency. The amplitude can be enhanced by heating the film at 150°C in air (oxidation) and removed by a similar treatment in a hydrogen atmosphere. This enhancement-removal cycle can be repeated reproducibly. The time required for saturation of the enhancement when the oxidation treatment was slowed down by annealing in a vacuum of 10−3 Torr instead of at atmospheric pressure was observed to be independent of film thickness, indicating that a volume-diffusion process is not involved. The apparent importance of surface oxidation suggests two possible mechanisms, valence exchange and exchange anisotropy, which may contribute to the linewidth temperature dependence. The discovery of a temperature-dependent linewidth in thin films which exhibits a maximum in the vicinity of 80°K and the identification of this dependence with a surface oxidation process are the primary results of this investigation.