Annealing experiments carried out on Ca-doped yttrium iron garnet in an O-reducing atmosphere revealed marked decreases in magnetization over the entire temperature range. Simultaneously, the electric resistivity and the electric activation energy significantly increased. This was analyzed and compared, within the framework of the Fe-O cluster model, with other situations in which compensating holes could be found. One was their occupation of hybridized eigen-energy levels of the cluster. In this case, it could be shown at which ions the holes tended to remain for a given energy level. It was found that the active holes remained localized mostly at O ions. The other situation involved hole localization in an attractive trap center. The latter was created at the missing O ion between the tetrahedral and octahedral Fe-O ionic clusters in the proximity of a dopant Ca2+ ion. For sufficiently shallow traps, their localized states could be considered within the framework of an H-like model. The ground state energy of the vacancy could thus be estimated; considering the dielectric constant of the host material and the effective mass of the hole as variational parameters. Communication between the tetrahedral and octahedral Fe-O clusters, with missing O between them, was assumed to be maintained via the s-d hybridization.

A Microscopic Model of Oxygen Vacancies in Ca-Doped YIG. A.Lehmann-Szweykowska, A.Szamer, R.J.Wojciechowski, R.Micnas, T.Lulek: Journal of Physics - Conference Series, 2006, 30, 278-85