Effects of synthesis methods on the structural and magnetic properties of double perovskite Sr2CrReO6 oxide powders

Double perovskite Sr2CrReO6 (SCRO) powders were prepared using a sol-gel process and molten-salt synthesis (MSS) method and then followed by annealing at different temperatures in N2 (or Ar) atmospheres. They were characterized by powder X-ray diffraction and then followed by structural Rietveld refinements. The results reveal that at room temperature all the SCRO powders crystallize in a tetragonal phase structure with space group of I4/m. The Cr/Re cationic ordering degrees (η) at B-site in the sol-gel derived SCRO powders annealed in Ar and N2 atmospheres, were about 68.9 % and 45.3 % respectively. The η values for the SCRO powders prepared by MSS method under the molar ratios of product-to-flux with 1:100, 1:80, and 1:50, were 67.4 %, 57.0 % and 54.3 %, respectively. All the SCRO powders exhibited ferromagnetic behaviors at room temperature and their saturation magnetization (MS) values at 2 K were in range of 0.52–0.67 μB/f.u., smaller than the theoretical value of 1.0 μB/f.u. That can be ascribed to the anti-site defects as well as the surface spin disorders in these SCRO powders. The sol-gel derived SCRO powders had a bead-like morphology and their average composition is slight Cr-rich and Re-deficient with a chemical formula of Sr2Cr1+xRe1−xO6+δ, whereas the SCRO powders prepared by MSS method exhibited a spherical morphology and their average composition is slight Cr-rich and Sr-deficient with a chemical formula of Sr2−yCr1+yReO6+δ. XPS spectra confirm a mixed valence states of Cr3+ and Cr6+ ions in the sol-gel derived SCRO powders, while only Cr3+ ions present in the SCRO powders prepared by MSS method. The Sr2+ ions and a mixed Re4+ and Re6+ ions exist in all the SCRO powders, and three kinds of oxygen species are present as lattice oxygen (O2-), adsorbed oxygens, and the oxygens in hydroxyl groups, respectively. The sol-gel derived SCRO powders had a higher MS but a smaller Hc in comparison with the powders prepared by MSS method, which enables them to have promising applications in future spintronic devices.