Orbital ordering and one-dimensional magnetic correlation in vanadium spinel oxides AV2O4 (A = Zn, Mg, or Cd)

TL;DR

This paper theoretically investigates the mechanisms behind two phase transitions in vanadium spinel oxides, revealing how orbital ordering influences magnetic frustration and induces one-dimensional magnetic correlations.

Contribution

It develops an effective spin-orbital-lattice model for vanadium spinel oxides and uses Monte Carlo simulations to explain the nature of their phase transitions.

Findings

Higher-temperature transition involves layered orbital ordering with Jahn-Teller distortion.

Lower-temperature transition results in antiferromagnetic spin ordering.

Intermediate phase features weakly-coupled antiferromagnetic chains.

Abstract

We present our theoretical results on the mechanism of two transitions in vanadium spinel oxides $A$V$_2$O$_4$ ($A$=Zn, Mg, or Cd) in which magnetic V cations constitute a geometrically-frustrated pyrochlore structure. We have derived an effective spin-orbital-lattice coupled model in the strong correlation limit of the multiorbital Hubbard model, and applied Monte Carlo simulation to the model. The results reveal that the higher-temperature transition is a layered antiferro-type orbital ordering accompanied by tetragonal Jahn-Teller distortion, and the lower-temperature transition is an antiferromagnetic spin ordering. The orbital order lifts the magnetic frustration partially, and induces spatial anisotropy in magnetic exchange interactions. In the intermediate phase, the system can be considered to consist of weakly-coupled antiferromagnetic chains lying in the perpendicular planes to the tetragonal distortion.