# Superexchange interactions between spin-orbit-coupled $j\!\approx\!1/2$ ions in oxides with face-sharing ligand octahedra

## TL;DR

This study uses ab initio calculations to reveal exceptionally strong antiferromagnetic interactions in face-sharing 5d and 4d oxide structures, highlighting their potential for novel quantum magnetic materials.

## Contribution

It provides the first detailed ab initio analysis of superexchange interactions in face-sharing ligand octahedra, showing larger values than in other geometries.

## Key findings

- Antiferromagnetic interactions up to 400 meV in idealized structures.
- Significant electron-lattice coupling effects.
- Potential for rich phase diagrams under strain and pressure.

## Abstract

Using ab initio wave-function-based calculations, we provide valuable insights with regard to the magnetic exchange in 5$d$ and 4$d$ oxides with face-sharing ligand octahedra, BaIrO$_3$ and BaRhO$_3$. Surprisingly strong antiferromagnetic Heisenberg interactions as large as 400 meV are computed for idealized iridate structures with 90$^{\circ}$ Ir-O-Ir bond angles and in the range of 125 meV for angles of 80$^{\circ}$ as measured experimentally in BaIrO$_3$. 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 5$d$/4$d$ orbitals and networks of face-sharing ligand cages. The strong electron-lattice couplings evidenced by our calculations suggest rich phase diagrams as function of strain and pressure, a research direction with much potential for materials of this type.