Spin and Orbital Order of the Vanadium Spinel MgV2O4

TL;DR

This study investigates the complex interplay of spin, lattice, and orbital degrees of freedom in MgV2O4, revealing a low-temperature magnetic structure with one-dimensional excitations and mixed orbital states.

Contribution

It provides detailed structural and magnetic characterization of MgV2O4, highlighting the role of trigonal distortion and spin-orbit coupling in its orbital ordering and magnetic properties.

Findings

Distortion from spinel structure at room temperature.

Antiferromagnetic chains with reduced magnetic moments below 42 K.

One-dimensional magnetic excitations observed via neutron scattering.

Abstract

We present a unique study of the frustrated spinel MgV2O4 which possesses highly coupled spin, lattice and orbital degrees of freedom. Using large single-crystal and powder samples, we find a distortion from spinel at room temperature (space group F-43m) which allows for a greater trigonal distortion of the VO6 octahedra and a low temperature space group (I-4m2) that maintains the mirror plane symmetry. The magnetic structure that develops below 42 K consists of antiferromagnetic chains with a strongly reduced moment while inelastic neutron scattering reveals one-dimensional behavior and a single band of excitations. The implications of these results are discussed in terms of various orbital ordering scenarios. We conclude that although spin-orbit coupling must be significant to maintain the mirror plane symmetry, the trigonal distortion is large enough to mix the 3d levels leading to a wave function of mixed real and complex orbitals.