Electronic structure of V$_4$O$_7$: charge ordering, metal-insulator transition and magnetism

TL;DR

This study uses ab initio calculations to analyze the electronic structure, charge and orbital ordering, and magnetic properties of V4O7 across its metal-insulator transition, revealing complex charge, orbital, and magnetic behaviors.

Contribution

It provides a detailed ab initio analysis of the charge, orbital, and magnetic ordering in V4O7, elucidating the mechanisms behind its metal-insulator transition and magnetic interactions.

Findings

Charge and orbital ordering occur below the transition.

V4+ dimers form spin singlets in the insulating phase.

Magnetic couplings are antiferromagnetic and vary across bonds.

Abstract

The low and high-temperature phases of V$_4$O$_7$ have been studied by \textit{ab initio} calculations. At high temperature, all V atoms are electronically equivalent and the material is metallic. Charge and orbital ordering, associated with the distortions in the V pseudo-rutile chains, occur below the metal-insulator transition. Orbital ordering in the low-temperature phase, different in V$^{3+}$ and V$^{4+}$ chains, allows to explain the distortion pattern in the insulating phase of V$_4$O$_7$. The in-chain magnetic couplings in the low-temperature phase turn out to be antiferromagnetic, but very different in the various V$^{4+}$ and V$^{3+}$ bonds. The V$^{4+}$ dimers formed below the transition temperature form spin singlets, but V$^{3+}$ ions, despite dimerization, apparently participate in magnetic ordering.