Magnetostatic mode spectra of uniaxial ferromagnets

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Abstract
The Damon‐Eshbach dispersion relation for magnetostatic modes in a rectangular platelet is expressed in terms of the permeability tensor of the magnetic medium and the consequences of a uniaxial easy‐plane anisotropy are investigated. The anisotropy modifies the critical angle between bulk and surface modes which results in the existence of bulk excitations within the series of DE‐surface modes. Two systems are analyzed. In the case of a ferromagnetic layer compound, the anisotropy is large compared with the demagnetizing field and the series of surface modes is replaced by a second series of volume modes. Recent measurements are reported on Ca‐doped YIG. Several hundred modes of forward and backward volume modes are in good agreement with the calculated dispersion function using the parameters of pure YIG and Hu = −250 Oe. It is suggested that a measured anisotropy profile along the film normal suppresses a few bulk modes within the series of surface modes and accounts for a gap observed on the low field side of the uniform resonance.