Magnetic and Structural Studies of Sc Containing Ruthenate Double Perovskites A₂ScRuO₆ (A = Ba, Sr)

Ruthenium-containing double perovskites A₂ScRuO₆ have been synthesized as polycrystalline powders and structurally characterized using a combination of synchrotron X-ray and neutron powder diffraction methods. When A = Ba, a hexagonal 6L perovskite structure is obtained if the synthesis is conducted at ambient pressure and a rock-salt ordered cubic structure is obtained if the sample is quenched from high pressures. The Sr oxide Sr₂ScRuO₆ is obtained with a rock-salt ordered corner sharing topology. Heat capacity and bulk magnetic susceptibility measurements show that the three oxides are antiferromagnets. Cubic Ba₂ScRuO₆ undergoes a metal-insulator transition near 270 K and hexagonal Ba₂ScRuO₆ is a semiconductor with an activation energy of 0.207 eV. The magnetic structures of the two rock-salt ordered double perovskites were established using powder neutron diffraction and are described by k = (0,0,1) and k = (0,0,0) for the Ba and Sr oxides, respectively, corresponding to type I antiferromagnetic structures, with ferromagnetic layers stacked antiferromagnetically. The ambient-pressure hexagonal polymorph of Ba₂ScRuO₆ has partial Sc-Ru ordering at both the face-sharing B₂O₉ dimer and corner-sharing BO₆ sites. The magnetic structure is described by k = (1/2,0,0) with the basis vector belonging to the irreducible representation Γ³.