Electronic structure and phase transition in V2O3:: Importance of 3d spin-orbit interaction and lattice distortion

The 3d electronic structure and phase transition in pure and Cr doped V2O3 are theoretically investigated in relation to the 3d spin-orbit interaction and lattice distortion. A model consisting of the nearest-neighbor V ion pair with full degeneracy of the 3d orbitals is studied within the many-body point of view. It is shown that each V ion with S = 1 spin state has a large orbital magnetic moment similar to0.7mu(B) and no orbital ordering occurs in the antiferromagnetic insulating (AFI) phase. The anomalous resonant Bragg reflection found in the AFI phase is attributed to the magnetic ordering. In the AFI and paramagnetic insulating (PI) phases. Jahn-Teller like lattice instability leads to tilting of the V ion pairs from the corundum c-axis and this causes large difference in the orbital occupation between the paramagnetic metal and the insulating phases. which is consistent with linear dichroic V 2p XAS measurements. To understand the AFI to PItransition, a model spin Hamiltonian is also proposed. The transition is found to be simultaneous order-disorder transition of the magnetic moments and tilting directions of the V ion pairs. Softening of elastic constant C-44 and abrupt change in short range spin correlations observed at the transition are also explained.