Influence of structural distortions on the Ir magnetism in Ba_2-xSr_xYIrO₆ double perovskites

We explore the relative strengths of spin orbit coupling and crystal field splitting in the Ir⁵⁺ compounds Ba_2-xSr_xYIrO₆. In the case of strong spin orbit coupling and regular Ir⁵⁺ octahedra, one expects a non-magnetic J=0 state; in the case of distorted octahedra where crystal field effects dominate, the t_2g manifold splits into a magnetic ground state. We report the results of continuously transitioning from the cubic Ba₂YIrO₆ double perovskite with ideal octahedra to the monoclinic Sr₂YIrO₆ double perovskite with distorted octahedra. We see no emergence of an enhanced Ir⁵⁺ magnetic moment in the series on increasing the structural distortions, as would have been the case for significant crystal field splitting. The near-constant magnetic moment observed through the Ba_2-xSr_xYIrO₆ series reinforces the notion that spin-orbit coupling is the dominant force in determining the magnetism of iridium-oxygen octahedra in perovskite-like structures.