Structure and Magnetic Properties of Sr2CoWO6: An Ordered Double Perovskite Containing Co2+(HS) with Unquenched Orbital Magnetic Moment

Abstract

Sr2CoWO6 perovskite has been prepared in polycrystalline form by solid-state reaction at 1150 °C. This material has been studied by high-resolution synchrotron X-ray and neutron powder diffraction (NPD), magnetic measurements, and differential scanning calorimetry (DSC). At room temperature, the crystal structure is tetragonal, space group I4/m, with a = 5.58277(1) Å and c = 7.97740(1) Å. The structure contains alternating CoO6 and WO6 octahedra, tilted in anti-phase by 7.24° in the basal ab plane along the [001] direction of the pseudocubic cell. This corresponds to the a0a0c- Glazer's notation as derived by Woodward for 1:1 ordering of double perovskites, consistent with space group I4/m. DSC and NPD measurements as a function of temperature indicate a structural transition from tetragonal to monoclinic (space group P21/n) at 260 K. At 2 K the cell parameters are a = 5.61267(8) Å, b = 5.58753(8) Å, c = 7.8994(1) Å, and β = 90.041(3)°. The structure contains alternating CoO6 and WO6 octahedra, tilted in-phase by 4.77° along the [001] direction of the pseudocubic cell and in anti-phase by 5.82° along the [010] and [100] directions. This corresponds to the a-a-c+ Glazer's notation as derived by Woodward for 1:1 ordering in double perovskites, consistent with space group P21/n. Magnetic and neutron diffraction measurements indicate an antiferromagnetic ordering below TN = 24 K. The magnetic moment calculated through the linear fit of the Curie−Weiss law at high temperatures (5.20 μB) indicates that the orbital contribution is unquenched at high temperatures, which is consistent with high-spin Co2+ (4T1g ground state) in a quasi-regular octahedral environment. As prepared, the sample is an electrical insulator. Magnetic and electrical properties and bond valence sums are consistent with the electronic configuration Co2+(3d7)−W6+(5d0).