Induction of colossal magnetoresistance in the double perovskite Sr2CoMoO6

Sr2CoMoO6 perovskite has been prepared in polycrystalline form by thermal treatment, in air, of previously decomposed citrate precursors. This material has been studied by X-ray (XRD) and neutron powder diffraction (NPD), thermal analysis, and magnetic, magneto-transport, and Hall effect measurements. At room temperature, the crystal structure is tetragonal with a space group l4/m, with a = 5.565 03(5) and c = 7.948 10(8) Angstrom. The crystal contains alternating CoO6 and MoO6 octahedra, tilted by degrees6.8 in the basal ab plane. Magnetic measurements indicate an antiferromagnetic ordering below T-N = 37 K. As prepared, the sample is an electrical insulator. The topotactic reduction of the stoichiometric sample, in H-2/N-2 flows, leads to oxygen-deficient double perovskites, Sr2COMoO6-delta, delta = 0.03 and 0.14. The magnetic behavior of the reduced samples suggests the presence of ferromagnetic domains characterized by Curie temperatures of T-C = 350-370 K. The conductivity dramatically increases upon H-2 reduction; the number of charge carriers, as determined by Hall effect measurements, are 1.7 x 10(-7) and 6 x 10(-6) electrons per unit cell for delta = 0.03 and 0.14 samples, respectively. Moreover, the reduced samples exhibit colossal magneto-resistance, as high as 30% at 12 K for H = 9T. Magnetic and magnetotransport results are consistent with a large component of itinerancy for down-spin Mo t(2g) electrons, injected through hydrogen reduction.