CALCULATION OF THE FERROMAGNETIC-RESONANCE LINEWIDTH OF BARIUM FERRITE

Two microscopic models have been proposed to explain the large intrinsic linewidth of barium ferrite. The first is a two-magnon scattering process due to an intrinsic disorder associated with the unique trigonal bipyramidal site in the crystal. [E. Tsantes and L. M. Silber, J. Appl. Phys. 63, 3350 (1988)]. The second is the Kasuya-LeCraw relaxation process [S. P. Marshall, J. B. Sokoloff, and C. Vittoria, IEEE Trans. Magn. MAG-25, 3491 (1989)]. Both of these processes involve modulation of the single-ion anisotropy. Analytical calculations using simplified models for the acoustic magnon and phonon spectra fail to account for the linewidths characteristic of barium ferrite. In order to understand both of these relaxation processes as they relate to barium ferrite, we have calculated the full phonon spectrum for this crystal based on the rigid-ion model. The calculated reflectivity compares well with the infrared reflectivity data that we have taken. Using phonon modes that we have calculated and the magnon modes calculated previously [S. P. Marshall and J. B. Sokoloff, J. Appl. Phys. 67, 2017 (1990)], we have calculated the ferromagnetic resonance linewidth on the basis of the Kasuya-LeCraw mechanism and two-magnon scattering by fluctuating 2b-site ions. We find that the trigonal-site disorder scattering mechanism is able to account for the observed magnitude of the linewidth.