Ferromagnetic Resonance Line Width in Yttrium Iron Garnet Single Crystals

Abstract

A study of ferromagnetic resonance line width in polished, single-crystal spheres of yttrium iron garnet is described. Wave-guide cavity perturbation techniques are used with samples 0.013 in. to 0.020 in. in diameter. An extremely narrow line width of 520 millioersteds (the full width) is observed at 9300 Mc/sec along the hard axis [100]. It is believed this is the narrowest resonance line yet reported on ferromagnetic materials. The line width is shown to be strongly influenced by the sample surface, with the line narrowing by over a factor of twenty as the polishing proceeds.The line width at 3000 Mc/sec on the same sample is 530 millioersteds. The approximate invariance of the line width for more than a three-to-one change in frequency is compared with the predictions of some recent theories of ferromagnetic resonance line width. The invariance of line width with frequency is also used to conclude that $\ensuremath{\lambda}\ensuremath{\omega}$ and ${T}_{2}$ in the Landau-Lifshitz and Bloch-Bloembergen equations of motion, respectively, are approximately constant over this frequency range.