Spin-spin correlations in the insulating and metallic phases of the Mott system V2O3

The magnetic response in V2O3 has been investigated using polarised neutron scattering with polarisation analysis. Measurements were carried out at th ree temperatures corresponding to the antiferromagnetic insulating ground s tate, the metallic phase and the high temperature metallic phase. At the fi rst order metal insulator transition there is a dramatic change in the magn etic response with the metallic and high temperature metallic phases being characterised by ferromagnetic spatial correlations of the paramagnetic res ponse. The establishment of ferromagnetic correlations at the metal insulat or transition accounts for the abrupt jump in the uniform susceptibility. I t is proposed that the differentiation of the V-V distances across the edge s of VO6 octahedra is of critical importance fur the change in electronic c onductivity but also for the establishment of the spatial correlations. The gradual high temperature evolution of the conductivity then occurs by the reduction in the vanadium d overlap brought about by thermal expansion. The first order reduction in atomic volume which occurs on the establishment o f the metallic phase results from an instability of the vanadium local mome nt arising from the change in electronic structure.