Abstract
The phenomenological propagation loss theory based on the Gilbert form of the equation of motion for the magnetization is clarified for surface wave modes and extended to include volume wave modes. For small numbers, the expression 76.4ΔH (dB/μs) is found to accurately give forward volume wave losses, but to underestimate both surface and backward volume wave losses at low frequencies. Here ΔH is the full ferromagnetic resonance linewidth. As an example, the surface and backward volume wave losses at 3 GHz in yttrium iron garnet are more accurately given by 99.3ΔH (dB/μs) for small wave numbers. For a fixed bias field, surface wave losses per unit time are shown to be constant with frequency across the passband, whereas volume wave losses per unit time have a quadratic frequency dependence. After a review of existing experimental results, it is concluded that further data is necessary for a definitive test of the theory.

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