Structural and magnetic properties of the osmium double perovskites Ba2-xSrxYOsO6

Abstract

The crystal and magnetic structures of double perovskites of the type Ba2-xSrxYOsO6 have been studied by synchrotron X-ray and neutron powder diffraction methods, bulk magnetic susceptibility measurements and X-ray absorption spectroscopy. The structures were refined using a combined neutron and synchrotron data set and are based on ordered array of corner sharing YO6 and OsO6 octahedra, with the Ba/Sr cations being completely disordered. The structure evolves from cubic to monoclinic as the Sr content is increased, due to the introduction of cooperative tilting of the octahedra. Bulk magnetic susceptibility measurements demonstrate the oxides are all antiferromagnets. The decrease in symmetry results in a, non-linear, increase in the Neel temperature. Low temperature neutron diffraction measurements of selected examples show these to be type-I antiferromagnets. X-ray absorption spectra collected at the Os L3- and L2-edges confirm the Os is pentavalent in all cases, and there is no detectable change in the covalency of the Os cation as the A-cation changes. Analysis of the L3:L2 branching ratio shows that the spin-orbit coupling is constant and insignificant across the series.