Structural, orbital, and magnetic order in vanadium spinels

TL;DR

This paper presents a theoretical model explaining the complex interplay of structural, orbital, and magnetic orders in vanadium spinels, highlighting the roles of spin-orbit coupling, Jahn-Teller effects, and frustration.

Contribution

It introduces a comprehensive theoretical framework that accounts for relativistic effects and collective phenomena in vanadium spinels, advancing understanding of their phase transitions.

Findings

Vanadium ions show ferroorbital order below the structural transition.

Magnetism can be described as two sets of antiferromagnetic chains with Ising anisotropy.

Magnetic order emerges at a tetracritical point.

Abstract

Vanadium spinels (ZnV_2O_4, MgV_2O_4, and CdV_2O_4) exhibit a sequence of structural and magnetic phase transitions, reflecting the interplay of lattice, orbital, and spin degrees of freedom. We offer a theoretical model taking into account the relativistic spin-orbit interaction, collective Jahn-Teller effect, and spin frustration. Below the structural transition, vanadium ions exhibit ferroorbital order and the magnet is best viewed as two sets of antiferromagnetic chains with a single-ion Ising anisotropy. Magnetic order, parametrized by two Ising variables, appears at a tetracritical point.