Ferrimagnetic Resonance in Rare-Earth-Doped Yttrium Iron Garnet. III. Linewidth

Measurements of ferrimagnetic resonance linewidth have been made for single crystals of yttrium iron garnet (YIG) doped with each of the $4f$ rare earths (except Ce, Gd, Pm, and Lu). Starting from the lowest temperatures, the linewidth increases to a maximum in the range 30 to 150^∘{}K, and then decreases. Some structure is apparent in these curves; they are anisotropic; and they are frequency dependent [at least in the case of YIG(Tb)]. The linewidths are discussed in terms of transitions within the ground multiplet of the rare-earth ions in the magnetic crystal.It seems possible to account for the general features of the data, in particular for the Tb case, by assuming that the rare-earth magnetization relaxes with a number of different relaxation times, some of which are comparable with the reciprocal of the microwave frequency.