Structural and magnetic properties of 4d and 5d perovskites

During the last years, the study of osmium-based oxides has attracted a lot of attention in materials science, since the properties of the 4d and particularly 5d oxides are expected to be extremely appealing. The increased spatial extent of the 4d/5d orbitals of the second/third-row transition-metal ions, with respect to the rather localized 3d orbitals of the first-row, gives rise to weaker Coulomb interactions. This leads to a greater level of splitting in the crystal field and consequently an increase in the sensitivity of these ions to lattice distortions, which present unusual electronic structures due to their characteristic spin-orbit coupling. For example, several interesting properties have been reported for pyrochlores, such as superconductivity in KOs₂O₆ (Tc = 9.6 K) and RbOs₂O₆ (Tc = 6.3 K) or metal–insulator (MI) transition at 225 K in the Cd₂Os₂O₇. Among the double perovskites, it is noteworthy to mention some examples, like the Sr₂CrOsO₆ oxide, which displays the highest Curie temperature (725 K) of the perovskite likestructure compounds, the recently described compounds Ca₂FeOsO₆ and Sr₂FeOsO₆, which undergoes a magnetic transition from ferromagnetic to antiferromagnetic when substituting Ca by Sr, or the FCC magnetically frustrated Ba₂YOsO₆ perovskite. The outstanding magnetic behavior of the osmium-based double perovskites raised the interest of searching new compounds and explores their physical properties. Therefore, in this work, we present a crystallographic and magnetic study of the solid solution Ba_2-xSr_xYOsO₆ (0 ≤ x ≤ 2) and compare this to the behavior in the closely related series Ba_2-xSr_xYRuO₆. Neutron powder diffraction experiments were performed at room temperature in order to investigate in detail the crystal structures. To determine the magnetic structure of the samples, NPD data were collected below the order magnetic temperature.