Magnetostructural effects and phase transition in Cr2O3 under pressure

We have successfully calculated the electronic and structural properties of chromia (Cr2O3) in the local spin density approximation. We predict a tran sformation from the corundum to the Rh2O3 (II) structure around 15 GPa in t he antiferromagnetic (AFM) phase as well as in the paramagnetic (PM) insula ting state which occurs above the Neel temperature (T-N) This transition is relevant to interpreting the optical anomalies observed in the absorption spectrum of ruby under pressure. We have modeled the structural properties of the PM state using a Landau-like expansion of the magnetostriction energ y. This treatment correctly describes the structural anomalies across T-N i n the corundum phase and indicates that the AFM and PM insulating states sh ould have distinct compressive behaviors.