Crystal and magnetic structure of the double perovskite Sr2CoUO6:: a neutron diffraction study

Sr2CoUO6 double perovskite has been prepared as a polycrystalline powder by solid-state reaction, in air. This material has been studied by X-ray, neutron powder diffraction (NPD) and magnetic measurements. At room temperature, the crystal structure is monoclinic, space group P2(1)/ n, Z = 2, with a = 5.7916( 2), b = 5.8034( 2), c = 8.1790( 3) Angstrom, beta = 90.1455(6)degrees. The perovskite lattice consists of a completely ordered array of CoO6 and UO6 octahedra, which exhibit an average tilting angle phi = 11.4degrees. Magnetic and neutron diffraction measurements indicate an antiferromagnetic ordering below T-N = 10 K. The low-temperature magnetic structure was determined by NPD, selected among the possible magnetic solutions compatible with the P2(1)/n space group, according with the group theory representation. The propagation vector is k = 0. A canted antiferromagnetic structure is observed below T-N = 10 K, which remains stable down to 3 K, with an ordered magnetic moment of 2.44(7) mu(B) for Co2+ cations. The magnetic moment calculated from the Curie Weiss law at high temperatures (5.22 mu(B)/f.u.) indicates that the orbital contribution is unquenched at high temperatures, which is consistent with high-spin Co2+ (T-4(1g) ground state) in a quasi-regular octahedral environment. Magnetic and structural features are consistent with an electronic configuration Co2+ [3d(7)] U6+ [Rn].