Theory for spin and orbital orderings in high-temperature phases in YVO₃

Motivated by the recent neutron-diffraction experiment on YVO₃, we consider a microscopic model where each V3+ ion is occupied by two 3d electrons of parallel spins with twofold-degenerate orbital configurations. The mean-field classical solutions of the spin-orbital superexchange model predicts an antiferro-orbital ordering at a higher temperature followed by a C-type antiferromagnetic spin ordering at a lower temperature. Our results are qualitatively consistent with the observed orbital phase transition at ∼200 K and the spin phase transition at ∼114 K in YVO₃.