Suppression of magnetism in Ba5AlIr2O11: interplay of Hund's coupling, molecular orbitals and spin-orbit interaction

TL;DR

This study investigates the electronic and magnetic properties of Ba5AlIr2O11, revealing that spin-orbit coupling and covalency suppress magnetism through metal-metal bonding, challenging previous charge-ordering explanations.

Contribution

It demonstrates that magnetism suppression in Ba5AlIr2O11 arises from spin-orbit interaction and covalency, not charge-ordering, highlighting a mechanism relevant to other 4d and 5d dimers.

Findings

Magnetic moment suppression is due to spin-orbit coupling and covalency.

Metal-metal bonds form, counteracting Hund's rule exchange.

The mechanism may apply to other 4d and 5d transition metal dimers.

Abstract

The electronic and magnetic properties of Ba$_5$AlIr$_2$O$_{11}$ containing Ir-Ir dimers are investigated using the GGA and GGA+SOC calculations. We found that strong suppression of the magnetic moment in this compound recently found in [J. Terzic {\it et al.}, Phys. Rev. B {\bf 91}, 235147 (2015)] is not due to charge-ordering, but is related to the joint effect of the spin-orbit interaction and strong covalency, resulting in the formation of metal-metal bonds. They conspire and act against the intra-atomic Hund's rule exchange interaction to reduce total magnetic moment of the dimer. We argue that the same mechanism could be relevant for other $4d$ and $5d$ dimerized transition metal compounds.