Coexisting charge and magnetic orders in the dimer-chain iridate Ba5AlIr2O11

TL;DR

This study synthesizes and investigates Ba5AlIr2O11, revealing complex charge and magnetic orders, phase transitions, and the influence of covalency and spin-orbit interactions on its magnetic state.

Contribution

It provides new insights into how strong covalency and spin-orbit interactions influence charge and magnetic orders in iridate dimer chains.

Findings

Structural phase transition at 210 K indicating enhanced charge order

Magnetic transition at 4.5 K resistant to magnetic fields but sensitive to pressure

Suppression of double exchange stabilizing a novel magnetic state

Abstract

We have synthesized and studied single-crystal Ba5AlIr2O11 that features dimer chains of two inequivalent octahedra occupied by tetravalent and pentavalent ions, respectively. Ba5AlIr2O11 is a Mott insulator that undergoes a subtle structural phase transition near 210 K and a magnetic transition at 4.5 K; the latter transition is surprisingly resistant to applied magnetic fields up to 12 T, but sensitive to modest applied pressure. All results indicate that the phase transition at 210 K signals an enhanced charge order that induces electrical dipoles and strong dielectric response near 210 K. It is clear that the strong covalency and spin-orbit interaction (SOI) suppress double exchange in Ir dimers and stabilize a novel magnetic state. The behavior of Ba5AlIr2O11 therefore provides unique insights into the physics of SOI along with strong covalency in competition with double exchange interactions of comparable strength.