PHASE TRANSITIONS IN INSULATING VANADIUM OXIDE

The magnetic phase transition from the paramagnetic to antiferromagnetic state in insulating V2O3 shows some very interesting features. Not only is the magnetic order ng pattern anomalous, but the magnetic transition shows other surprises: I) the magnetic and orbital ordering occur at the same transition temperature; II) the transition is strongly first order; III) above the transition temperature, neutron scattering observes features in wave vectors different from the ordering wave vector. We study this system using the recently proposed S = 2 bond model (Phys. Rev. Lett.85, 1714 (2000)) for insulating V2O3. We show that this model not only explains the anomalous magnetic ordering, but also resolves the other questions associated with the magnetic phase transition (Phys. Rev. Lett.86, 5743 (2001)). We further point out the possibility of changes in the phase transition phenomenology in presence of a magnetic field, and another orbital phase transition at lower temperatures.