Frequency dependence of the ferromagnetic resonance linewidth of barium ferrite

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Abstract
Ferromagnetic resonance was measured in both a swept frequency mode of operation, in which the magnetic field was fixed, and a field swept mode, using field modulation techniques. Single-crystal spheres of 0.381, 0.305, and 0.483 mm in diameter were inserted in the waveguide and transmission was observed in the measurement. The g values for all the spheres averaged to 2.052±0.011 and the uniaxial anisotropy field was 16.4 kOe.Our measurements show that the linewidth of barium ferrite is nearly independent of resonant frequency from 48 to 105 GHz. This is in disagreement with the Kasuya–LeCraw two-magnon–one-phonon mechanism, which would predict a linewidth linear with the resonant frequency. Previous measurements [J. Magn. Magn. Mater. 54-57, 1141 (1986); IEEE Trans. Magn. MAG-22, 984 (1986)], however, show a strong temperature dependence, which rules out magnon scattering from static defects as the primary contributor to the intrinsic linewidth. These results are consistent with a single scattering process in which the uniform precession magnon is scattered into the continuum of magnons by time-dependent fluctuations of the trigonal symmetry ion between two equilibrium sites on either side of the mirror plane [J. Appl. Phys. 63, 3350 (1988)]. This process differs from the usual two-magnon scattering in that the scattering mechanism is time dependent, and, therefore, the magnon frequency need not be conserved in the process.