Transition-metal ordered double-perovskites: Half-metallic oxides with high Curie temperatures

Full Text:The interest in transition-metal double perovskites, A2BB'O6 (A-alkaline earth ions, B and B' - transition metal ions) has been driven by the discovery of low-field negative magnetoresistance exhibited up to room temperature (RT) by polycrystalline samples of some members of this family. Those members are regarded as half-metals, for which the Fermi level resides in a fully spin-polarized band. Their Curie temperatures are far above RT. When perfectly ordered, their magnetization is an integral number of Bohr magnetrons/formula unit. Their zero-field conductivity (''(T)) and magneto-conductivity (MC) may be dominated by spin-polarized inter-grain tunneling. The remarkable linearity of σ(T) from liquid He temperatures up to RT at least, found by us for various samples of sintered and granular Sr2FeMoO6, has motivated our study of additional members of this family. We report on selected results of our measurements of magnetization, thermopower, σ. MC and non-linear conductivity with, high pulsed electric currents, carried out on polycrystalline samples of Sr2FeMoO6, Sr2FeReO6, Sr2CrReO6, Sr2CrMoO6, Srv2CrWO6 and Sr3Cr2WO9