Orbital order and electron itinerancy in CoV$_{2}$O$_{4}$ and Mn$ _{0.5} $Co$ _{0.5} $V$_{2}$O$_{4}$ from first principles

TL;DR

This study uses first principles calculations to analyze orbital order and electron itinerancy in CoV₂O₄ and Mn₀.₅Co₀.₅V₂O₄, revealing how structural phases influence orbital states and how doping affects electron mobility.

Contribution

It provides a detailed first-principles investigation of orbital order states and electron itinerancy in related vanadate spinels, highlighting the impact of structural symmetry and doping.

Findings

Tetragonal phase with I4₁/amd symmetry has complex orbital order with large orbital moments.

I4₁/a symmetry phase exhibits real orbital order with quenched orbital moments.

Electron itinerancy increases from MnV₂O₄ to CoV₂O₄ while orbital order remains stable.

Abstract

In view of the recent experimental predictions of a weak structural transition in CoV$_{2}$O$_{4}$ we explore the possible orbital order states in its low temperature tetragonal phases from first principles density functional theory calculations. We observe that the tetragonal phase with I4$_1/amd$ symmetry is associated with an orbital order involving complex orbitals with a reasonably large orbital moment at Vanadium sites while in the phase with I4$_1/a$ symmetry, the real orbitals with quenched orbital moment constitute the orbital order. Further, to study the competition between orbital order and electron itinerancy we considered Mn$_{0.5}$Co$_{0.5}$V$_{2}$O$_{4}$ as one of the parent compounds, CoV$_{2}$O$_{4}$, lies near itinerant limit while the other, MnV$_{2}$O$_{4}$, lies deep inside the orbitally ordered insulating regime. Orbital order and electron transport have been investigated using first principles density functional theory and Boltzmann transport theory in CoV$_{2}$O$_{4}$, MnV$_{2}$O$_{4}$ and Mn$_{0.5}$Co$_{0.5}$V$_{2}$O$_{4}$. Our results show that as we go from MnV$_{2}$O$_{4}$ to CoV$_{2}$O$_{4}$ there is enhancement in the electron's itinerancy while the nature of orbital order remains unchanged.