Covalency and vibronic couplings make a nonmagnetic j=3/2 ion magnetic

TL;DR

This paper investigates how covalency and vibronic couplings influence the magnetic properties of 4d^1 and 5d^1 ions in double-perovskite systems, revealing complex interactions that challenge classical notions of nonmagnetic j=3/2 states.

Contribution

It provides a detailed analysis of the electronic structure and magnetic behavior of 4d^1 and 5d^1 ions, highlighting the roles of covalency and electron-lattice interactions in determining magnetic ground states.

Findings

Magnetic moments in 4d^1 ions arise from hybridization and Jahn-Teller effects.

In 5d^1 ions, covalency primarily influences magnetic properties.

Charge imbalance allows tuning of orbital energy levels.

Abstract

For 4$d^1$ and 5$d^1$ spin-orbit-coupled electron configurations, the notion of nonmagnetic j=3/2 quartet ground state discussed in classical textbooks is at odds with the observed variety of magnetic properties. Here we throw fresh light on the electronic structure of 4$d^1$ and 5$d^1$ ions in molybdenum- and osmium-based double-perovskite systems and reveal different kinds of on-site many-body physics in the two families of compounds: while the sizable magnetic moments and $g$ factors measured experimentally are due to both metal $d$-ligand $p$ hybridization and dynamic Jahn-Teller interactions for 4$d$ electrons, it is essentially $d$-$p$ covalency for the 5$d^1$ configuration. These results highlight the subtle interplay of spin-orbit interactions, covalency and electron-lattice couplings as the major factor in deciding the nature of the magnetic ground states of 4$d$ and 5$d$ quantum materials. Cation charge imbalance in the double-perovskite structure is further shown to allow a fine tuning of the gap between the $t_{2g}$ and $e_g$ levels, an effect of much potential in the context of orbital engineering in oxide electronics.