Magnetic correlations and quantum criticality in the insulating antiferromagnetic, insulating spin liquid, renormalized Fermi liquid, and metallic antiferromagnetic phases of the Mott system V2O3

Magnetic correlations in all four phases of pure and doped vanadium sesquio xide (V2O3) have been examined by magnetic thermal-neutron scattering. Spec ifically, we have studied the antiferromagnetic and paramagnetic phases of metallic V2-yO3, the antiferromagnetic insulating and paramagnetic metallic phases of stoichiometric V2O3, and the antiferromagnetic and paramagnetic phases of insulating V1.944Cr0.056O3. While the antiferromagnetic insulator can be accounted for by a localized Heisenberg spin model, the long-range order in the antiferromagnetic metal is an incommensurate spin-density wave , resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations with a "single lobe'' spectrum in the Stoner electron-hole continuum. Furthermore, our re sults in metallic V2O3 represent an unprecedentedly complete characterizati on of the spin fluctuations near a metallic quantum critical point, and pro vide quantitative support for the self-consistent renormalization theory fo r itinerant antiferromagnets in the small moment limit. Dynamic magnetic co rrelations for (h) over bar omega<k(B)T in the paramagnetic insulator carry substantial magnetic spectral weight. However, they are extremely short-ra nged, extending only to the nearest neighbors. The phase transition to the antiferromagnetic insulator, from the paramagnetic metal and the paramagnet ic insulator, introduces a sudden switching of magnetic correlations to a d ifferent spatial periodicity which indicates a sudden change in the underly ing spin Hamiltonian. To describe this phase transition and also the unusua l short-range order in the paramagnetic state, it seems necessary to take i nto account the orbital degrees of freedom associated with the degenerate d orbitals at the Fermi level in V2O3. [S0163-1829(98)06443-1].