Anomalies of ferromagnetic resonance in garnets and their relation to the magnetization process

X- and L-band ferromagnetic resonance (FMR) measurements were made for a [111]-film sample of a bismuth-substituted garnet (YbTbBi)(3)Fe5O12. From the angular variation of the FMR signal, magnetic parameters have been determined as uniaxial anisotropy constant K-u = 4.17 x 10(3) J/m(3), cubic anisotropy constant K-1 = -6.7 x 10(2) J/m(3), and gyromagnetic ratio gamma/2 pi = 23.9 GHz/T. Besides the usual FMR signal, anomalous-shaped features have been observed in the range 100-150 mT. The occurring fields of the features do not depend on the microwave frequency employed. The features always appear at the characteristic fields of the magnetization process such as the saturation-complete field under increasing field and the saturation-breakdown held under decreasing field. Faraday rotation measurements were also made to confirm the coincidence between the characteristic fields of the magnetization curve and the anomalous FMR features. These results establish that the anomalous features reflect the magnetization process of the sample. Such features so far have not been known. The origin of the anomalous features is also considered. (C) 1998 American Institute of Physics.