Half-Metallicity in Pb2CoReO6Double Perovskite and High Magnetic Ordering Temperature in Pb2CrReO6Perovskite.

Pb2MReO6(M = Co, Cr) perovskites were preparedby high pressure–high temperature method. Rietveld refinementsof synchrotron powder X-ray diffraction show that the crystal structureof Pb2CoReO6is 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 furtherclarified by X-ray absorption spectroscopy that establishes formaloxidation states in these phases as Pb2Co2+Re6+O6and Pb2Cr3+Re5+O6. Pb2CrReO6is a simple perovskitewith a high magnetic ordering temperature of 643 K. Pb2CoReO6is a double perovskite with −23% high fieldnegative magnetoresistance at 10 K and 9 T. First-principles calculationsof Pb2CoReO6indicate a half metallic electronicstructure. [ABSTRACT FROM AUTHOR]