Anomalous resonance field shifts in amorphous Gd.37Al.63

Abstract

An anomalous frequency independent magnetic resonance field shift has been observed in amorphous Gd.37Al.63 thin film alloy. Data are reported at frequencies of 9.2, 23.0, and 34.9 GHz and over a range of temperature from 4.2 K to 100 K. Below about 50 K the magnitude of the applied field required for resonance begins to deviate significantly from the value expected from the bulk magnetization of the amorphous material. An increase in the linewidth of nearly the same magnitude as the deviation of the ’’internal field’’ is also observed. The magnitude of the resonance field shift and the change in the linewidth are both insensitive to changes in the operating frequency. It is proposed that the observed resonance field shifts can be attributed to the excitation of spinwave modes localized or ’’pinned’’ within small ferromagnetic regions. The observed increase in the linewidth is then explained within the framework of this model as being due to changes in the demagnetizing fields associated with each of the variously shaped ferromagnetic clusters.