ENHANCED MICROWAVE MAGNETIC PROPERTIES-IN NONSTOICHIOMETRIC YTTRIUM IRON GARNETS FOR HIGH-POWER APPLICATIONS

A nonstoichiometric 3 mol% Fe-deficient deficient yttrium iron garnet composition (Y3Fe4.85O12) chemically-modified with Si and Mn was inves tigated with regard to microstructure characteristics and microwave ma gnetic properties for high power applications. The two additives, Si a nd Mn were added to the garnet composition by a chemical method utiliz ing a sol-gel reaction. The samples were sintered at 1500 degrees C fo r 3 hrs in O-2. An increase;,in Si content tends to increase bulk dens ity and to decrease grain size. An yttrium-rich second phase found in pure Y3Fe4.85O12 was observed to disappear with a sufficient amount of the additives. The improved microstructural characheristics were beli eved to contribute to the enhanced microwave magnetic properties of th e garnets. For example, spin wave line width, Delta H-k, which is a ke y 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.