Microwave Properties of Nonstoichiometric Polycrystalline Yttrium Iron Garnet

Abstract

An investigation has been made of the microwave properties of nonstoichiometric yttrium iron garnet ranging from 31% iron excess through stoichiometric to 12% yttrium excess. No ion substitution in the garnet lattice is observed. All material in excess of stoichiometric proportions goes into ceramic second phases. The phases observed are perovskite (YFeO3) for yttrium excess, hematite (Fe2O3) for iron-excess samples fired in oxidizing atmospheres, and magnetite (Fe3O4) for iron-excess samples fired in neutral atmospheres. On the basis of the assumption that all excess material goes into the appropriate ceramic second phase, we may account for the behavior of the saturation magnetization, spectroscopic splitting factor, and linewidth as a function of composition. It is found that the linewidth is strongly narrowed by the large magnetization as predicted by Geschwind and Clogston. The behavior of the dielectric constant can be explained, at least qualitatively, by a theory of Wagner and Sillars which considers particles of one dielectric material imbedded in a matrix of another. The behavior of the dielectric loss tangent is not understood and cannot be accounted for by this theory.