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Abstract

Using ab initio wave-function-based calculations, we provide valuable insights with regard to the magnetic exchange in 5d and 4d oxides with face-sharing ligand octahedra, BaIrO3 and BaRhO3. Surprisingly strong antiferromagnetic Heisenberg interactions as large as 400 meV are computed for idealized iridate structures with 90 degrees Ir-O-Ir bond angles and in the range of 125 meV for angles of 80 degrees as measured experimentally in BaIrO3. These estimates exceed the values derived so far for corner-sharing and edge-sharing systems and motivate more detailed experimental investigations of quantum magnets with extended 5d/4d orbitals and networks of face-sharing ligand cages. The strong electron-lattice couplings evidenced by our calculations suggest rich phase diagrams as a function of strain and pressure, a research direction with much potential for materials of this type.