Enhanced microwave magnetic properties in nonstoichiometric yttrium iron garnets for high power applications

A nonstoichiometric 3 mol% Fe-deficient yttrium iron garnet composition (Y₃Fe_4.85O₁₂) chemically-modified with Si and Mn was investigated with regard to microstructure characteristics and microwave magnetic properties for high power applications. The two additives, Si and Mn were added to the garnet composition by a chemical method utilizing a sol-gel reaction. The samples were sintered at 1500°C for 3 hrs in O₂. An increase in Si content tends to increase bulk density and to decrease grain size. An yttrium-rich second phase found in pure Y₃Fe _4.85O₁₂ was observed to disappear with a sufficient amount of the additives. The improved microstructural characteristics were believed to contribute to the enhanced microwave magnetic properties of the garnets. For example, spin wave line width, ΔH_k, which is a key factor for this application, was found to increase from 3.1 Oe to 12.6 Oe by adding 0.6 wt% SiO₂ and 0.15 wt% MnO₂. This can be attributed to smaller grain size and elimination of the Y-rich phase