Doped Sr 2 FeIrO 6 -Phase Separation and a J eff ≠ 0 State for Ir 5

High-resolution synchrotron X-ray and neutron powder diffraction data demonstrate that, in contrast to recent reports, Sr FeIrO adopts an I1̅ symmetry double perovskite structure with an a b c tilting distortion. This distorted structure does not tolerate cation substitution, with low levels of A-site (Ca, Ba, La) or Fe-site (Ga) substitution leading to separation into two phases: a stoichiometric I1̅ phase and a cation-substituted, P2 / n symmetry, a a c distorted double perovskite phase. Magnetization, neutron diffraction, and Fe Mössbauer data show that, in common with Sr FeIrO , the cation substituted Sr A Fe Ga IrO phases undergo transitions to type-II antiferromagnetically ordered states at T ∼ 120 K. However, in contrast to stoichiometric Sr FeIrO , cation substituted samples exhibit a further magnetic transition at T ∼ 220 K, which corresponds to the ordering of J ≠ 0 Ir centers in the cation-substituted, P2 / n symmetry, double perovskite phases.