Microwave losses induced by tetravalent iron in divalent ion substituted YIG epilayers

Microwave losses have been studied in two series of divalent cation-substituted yttrium iron garnet epilayers, Ca:YIG and Mg:YIG. Since CaO dissolves completely while MgO dissolves only partially in the fluxed melt, the magnetic losses caused by the Fe⁴⁺ions induced in the garnet lattice reach quite different magnitudes. Using microwave resonance and film etching, the concentration profiles of several Ca:YIG films have been studied. The effective gyromagnetic ratio of Ca:YIG films suggests that the Fe⁴⁺ion is located on the tetrahedral sites until a concentration threshold is obtained after which it starts to occupy the octahedral sites. In Mg:YIG films, due to the low concentration of Mg ions, only the tetrahedral sites are occupied. An experiment of the chemical sensitivity of a Ca-rich YIG film to reduction and oxydation solutions is also reported.