Ba₃CuOs₂O₉ and Ba₃ZnOs₂O₉, a comparative study

Highlights: • Hexagonal triple perovskite Ba₃CuOs₂O₉ and Ba₃ZnOs₂O₉ were synthesized. • The magnetic properties of Ba₃CuOs₂O₉ are dominated by Cu²⁺. • Ba₃ZnOs₂O₉ indicates strong antiferromagnetic correlations within the Os₂O₉ dimer. - Abstract: Polycrystalline samples of Ba₃CuOs₂O₉ and Ba₃ZnOs₂O₉ were synthesized by solid-state reactions. Ba₃CuOs₂O₉ crystallizes in Cmcm, while Ba₃ZnOs₂O₉ adopts the hexagonal space group P6₃/mmc. Both the crystal structures consist of face-sharing Os-centered octahedra forming dimer-like Os₂O₉ units, which are interconnected by corner-sharing CuO₆, or ZnO₆ octahedra, respectively. In Ba₃CuOs₂O₉, the CuO₆ octahedra show a characteristic Jahn-Teller distortion. Both, Ba₃CuOs₂O₉ and Ba₃ZnOs₂O₉, are electrically insulating. Magnetic and specific heat measurements confirm that Ba₃CuOs₂O₉ is antiferromagnetically ordered below 47 K. Analysis of the magnetic data indicated that its magnetic properties are dominated by Cu²⁺ ions. The magnetic susceptibility of Ba₃ZnOs₂O₉ is weakly temperature-dependent with a broad maximum ≈ 280 K, indicating the presence of strong exchange interactions within the Os₂O₉ dimer. The residual magnetic susceptibility at low temperatures also suggests the presence of appreciable exchange coupling between the dimers.