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Measurements of the position and linewidth of the main resonance in the spin-wave spectra of 80% Ni-20% Fe evaporated films 150 to 3200 Å thick at frequencies from 0.8 to 4.0 GHz, at room temperature and with the static magnetic field perpendicular to the film plane have been performed. The center field for resonance was independent of thickness and consistent with the Kittel resonance condition for the uniform precession. The linewidth was about 30 Oe (measured as the field separation of inflection points on the absorption curve), independent of film thickness and frequency. The linewidth data have been compared to previous data for resonance with the static field parallel to the film plane and interpreted in terms of relaxation processes for the uniform precession. In general, frequency-swept linewidths, not field-swept linewidths, are proportional to the relaxation rate and are the quantities which should be compared. The frequency-swept linewidth for perpendicular resonance is equal to that obtained for parallel resonance in films thinner than 500 Å. This result indicates that two-magnon scattering between the uniform precession mode and spin-wave states for which the exchange energy term is large (wavenumber k appreciably different from zero) does not contribute to the perpendicular resonance linewidth and is the origin of the linewidth increase with thickness for parallel resonance. It appears that scattering to states with k≈0 and exchange conductivity broadening are the most reasonable sources for the residual 30 Oe linewidth.
Carl E. Patton (Sat,) studied this question.