Structure and magnetism of LaxSr2−xCo0.5Ir0.5O4−yHy (0 < x < 1) iridium-containing oxyhydride phases

Abstract

Ruddlesden-Popper oxide phases in the La_xSr_2−xCo_0.5Ir_0.5O₄ (0 < x < 1) solid solution can be converted to the corresponding La_xSr_2−xCo_0.5Ir_0.5O_4−yH_y oxyhydride phases, by topochemical reaction with LiH, in which the hydride ions are substituted exclusively onto the equatorial anion sites of the host framework. Analysis reveals that oxyhydride phases in the range 0.5 < x < 1 adopt La_xSr_2−xCo_0.5Ir_0.5O_2+xH_2−x compositions which maintain a constant Co¹⁺, Ir³⁺ oxidation-state combination (confirmed by Co K-edge XANES data), with the presence of low-spin d⁶ Ir³⁺ being consistent with the covalent stabilization of the metastable oxyhydride phases via strong Ir–H σ-bonds. Phases at the lanthanum-poor end of the solid solution (x < 0.5) adopt La_xSr_2−xCo_0.5Ir_0.5O_4−yH_y compositions with lower hydride concentrations (y < 1.5). Magnetisation and μSR data indicate that all the La_xSr_2−xCo_0.5Ir_0.5O_4−yH_y oxyhydride phases exhibit strong magnetic frustration, attributed to the large-scale cation and anion disorder, and resulting in glassy magnetic behaviour at low temperature.