Structural transition and orbital glass physics in near itinerant CoV2O4

TL;DR

This study reveals a weak structural transition and orbital glass state in CoV2O4, supported by neutron scattering data showing a spin gap and local orbital distortions, highlighting complex interplay between structure and magnetism.

Contribution

It provides the first direct evidence of a structural phase transition and orbital glass behavior in CoV2O4 through neutron scattering measurements.

Findings

Identification of a weak first-order structural transition at 90 K.

Observation of a spin gap of approximately 1.25 meV at low temperature.

Evidence supporting the orbital glass state below the transition temperature.

Abstract

The ferrimagnetic spinel $\mathrm{CoV_2O_4}$ has been a topic of intense recent interest, both as a frustrated insulator with unquenched orbital degeneracy and as a near-itinerant magnet which can be driven metallic with moderate applied pressure. Here, we report on our recent neutron diffraction and inelastic scattering measurements on powders with minimal cation site disorder. Our main new result is the identification of a weak ($\frac{\Delta a}{a} \sim 10^{-4}$), first order structural phase transition at $T^*$ = 90 K, the same temperature where spin canting was seen in recent single crystal measurements. This transition is characterized by a short-range distortion of oxygen octahedral positions, and inelastic data further establish a weak $\Delta\sim 1.25 meV$ spin gap at low temperature. Together, these findings provide strong support for the local orbital picture and the existence of an orbital glass state at temperatures below $T^*$.