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 a 0 a 0 c - 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 T N = 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).

Effects of chemical pressure on the magnetic ground states of the osmate double perovskitesSrCaCoOsO6andCa2CoOsMorrow1, Yan2, McGuire3 et al. 2015Phys. Rev. B387410View full textAdd to dashboardCite

“…The average bond lengths for both CoO 6 and OsO 6 octahedra are comparable to those found in Sr 2 CoOsO 6 [11], as well as other double perovskite oxides containing Os 6+ or high spin Co 2+ [23,24], kOe. The relative sign of the XMCD signal, shown as in Figure 4, is reversed between Co and Os, indicating that the moments localized on these elements are oriented antiparallel to one another.…”

“…Co moment (see [17] contribution that increases the cobalt moment more than the negative orbital contribution decreases the osmium moment [23]. No discernible anomalies are apparent in the heat capacity with or without an applied field of 80 kOe, as measured by a PPMS and shown in Figure 6b, nor is any magnetic scattering due to long range ordering apparent in the 10 K neutron powder diffraction pattern shown in Figure 6c.…”

Study of half-metallic behavior in Sr2CoWO6 perovskite by ab initio DFT calculations

“…We obtain lattice parameters a ¼ 5.531 Å and c ¼ 7.860 Å , which are in accordance with experimental results reported in Ref. [6].…”

“…The extensive half-metallicity studies in double perovskite materials are related with the probable technological applications in spintronic devices, such as spin valves, sources for spin polarized electrons and magnetic information storage systems. The aim of this work is to carry out a detailed ab initio theoretical study of the complex perovskite Sr 2 CoWO 6 compound, which was experimentally analyzed and reported as an antiferromagnetic half-metallic material with low Ne´el temperature (24 K) [6]. …”

X-ray diffraction and Raman spectroscopy studies of temperature and composition induced phase transitions in Ba2−xSrxZnWO6 (0≤x≤2) double perovskite oxides

“…Most investigations on A 2 BWO 6 (A = Ba, Sr, B = Co, Ni) [20][21][22][23] have employed X-ray powder diffraction, neutron powder diffraction, synchrotron X-ray diffraction techniques to probe the global structure of the materials using the Rietveld analysis.…”