Half-Metallicity in Pb2CoReO6 Double Perovskite and High Magnetic Ordering Temperature in Pb2CrReO6 Perovskite

Pb2MReO6 (M = Co, Cr) perovskites were prepared by high pressure high temperature method. Rietveld refinements of synchrotron powder X-ray diffraction show that the crystal structure of Pb2CoReO6 is trigonal (space group R-3) with almost complete ordering of Co and Re cations, while Pb2CrReO6 (space group Pm-3m) is a cubic perovskite with one single site for Cr and Re atoms. The difference between the symmetry and the degree of order was further clarified by X-ray absorption spectroscopy that establishes formal oxidation states in these phases as Pb2Co2+Re6+O6 and Pb2Cr3+Re5+ O-6. Pb2CrReO6 is a simple perovskite with a high magnetic ordering temperature of 643 K. Pb2CoReO6 is a double perovskite with 23% high field negative magnetoresistance at 10 K and 9 T. First-principles calculations of Pb2CoReO6 indicate a half metallic electronic structure.