DRAMATIC SWITCHING OF MAGNETIC EXCHANGE IN A CLASSIC TRANSITION-METALOXIDE - EVIDENCE FOR ORBITAL ORDERING

Spin correlations in metallic and insulating phases of V2O3 and its de rivatives are investigated using magnetic neutron scattering. Metallic samples have incommensurate spin correlations varying little with hol e doping. Paramagnetic insulating samples have, spin correlations only among near neighbors. The transition from either of these phases into the low temperature insulating antiferromagnetic phase is accompanied by an abrupt change of dynamic magnetic short range, order. Our resul ts support the idea that the transition into the antiferromagnetic ins ulator is also an orbital ordering transition.