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

Abstract

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 P2₁/n, Z = 2, with a = 5.7916(2), b = 5.8034(2), c = 8.1790(3) Å, β = 90.1455(6)°. The perovskite lattice consists of a completely ordered array of CoO₆ and UO₆ octahedra, which exhibit an average tilting angle φ = 11.4°. 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 P2₁/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) µ_B for Co²⁺ cations. The magnetic moment calculated from the Curie–Weiss law at high temperatures (5.22 µ_B/f.u.) indicates that the orbital contribution is unquenched at high temperatures, which is consistent with high-spin Co²⁺ (⁴T_1g ground state) in a quasi-regular octahedral environment. Magnetic and structural features are consistent with an electronic configuration Co²⁺[3d⁷]–U⁶⁺[Rn].