Magnetic order and ice rules in the multiferroic spinel FeV2O4

TL;DR

This neutron diffraction study of FeV2O4 reveals complex magnetic and orbital ordering, including ice-rule behavior in vanadium spins, across multiple structural and magnetic phase transitions.

Contribution

It provides detailed insights into the spin and orbital orderings in FeV2O4, highlighting the ice-rule behavior in vanadium spins, which is novel for this class of materials.

Findings

Confirmation of three structural phase transitions.

Sequential collinear and canted ferrimagnetic transitions.

Ice-rule behavior in vanadium spin ordering.

Abstract

We present a neutron diffraction study of FeV2O4, which is rare in exhibiting spin and orbital degrees of freedom on both cation sublattices of the spinel structure. Our data confirm the existence of three structural phase transitions previously identified with x-ray powder diffraction, and reveal that the lower two transitions are associated with sequential collinear and canted ferrimagnetic transitions involving both cation sites. Through consideration of local crystal and spin symmetry, we further conclude that Fe2+ cations are ferro-orbitally ordered below 135K and V3+ orbitals order at 60K in accordance with predictions for vanadium spinels with large trigonal distortions and strong spin-orbit coupling. Intriguingly, the direction of ordered vanadium spins at low temperatures obey `ice rules' more commonly associated with the frustrated rare-earth pyrochlore systems.