Superexchange and iron valence control by off-stoichiometry in yttrium iron garnet thin films grown by pulsed laser deposition

Controlled off-stoichiometric single phase polycrystalline yttrium iron garnet (YIG) thin films have been grown by pulsed laser deposition, adjusting the oxygen partial pressure P(O2) between 5 and 400 mTorr. Atomic stoichiometry by RBS shows an oxygen deficiency for P(O2) < P(stoich) and iron and yttrium deficiency for P(O2)> P(stoich). P(stoich)=30 mTorr refers to films showing magnetic and structural properties of the bulk stoichiometric YIG. Curie temperature T, and saturation magnetization 4 pi Ms decreased for P(O2)< P(stoich), whereas a new part of the YIG phase diagram is explored for P(O2)> P(stoich): Increase of Tc (up to +10%) and of 4 pi Ms (up to +20%) and lattice parameter compression. Microscopic interpretation is given in terms of superexchange interaction and creation and site selectivity of iron vacancies. (c) 2005 American Institute of Physics.