Frequency dependence of microwave magnetic resonance in the spin glassGd37Al63

Further data, completing an earlier report, are presented on the frequency and temperature dependence of the microwave magnetic resonance of an amorphous ${\mathrm{Gd}}_{37}$ ${\mathrm{Al}}_{63}$ film, which shows spin-glass properties. The data are analyzed according to a recent exchange-narrowing model in the temperature range above the freezing temperature. The $g$ shift is found to be frequency independent in this range, in support of the model. An anisotropy field of order $0.3\left(4\pi M\right)$ is also found in this range. Below the freezing temperature the frequency dependence reveals a changeover to a different kind of behavior, better described by a local field than by a $g$ shift.