Natural Spectrum of Polycrystalline YIG as a Function of Density

Abstract
The initial permeability of polycrystalline yttrium iron garnet has been measured as a function of density at frequencies from 5 kc/sec to 7.5 Gc/sec. The samples were prepared by grinding very pure single crystals into a powder and then pressing and sintering. The samples of highest density have two absorption peaks that occur at approximately 1 Mc/sec and 200 Mc/sec. This is in very good agreement with observations on polycrystalline samples prepared with coprecipated powders but not with those prepared with raw oxides. The separation between the two absorption peaks decreases as the sample density decreases, until ultimately only one peak is observed in a sample with 72% density. The results are interpreted in terms of the changing sample porosity.