Anisotropic hyperfine coupling in vanadium oxides

We have investigated orbital occupancies in metallic states of the vanadium oxides by 51V NMR measurements on the single crystals of V2O3, K2V8O16, and LiV2O4, having ground states of an antiferromagnetic Mott insulator, a spin singlet insulator, and a heavy-mass Fermi liquid, respectively. The Knight shift K vs the magnetic susceptibility plots for the principal axes give the axially anisotropic and isotropic parts of the hyperfine coupling constant, Aax and Aiso In V2O3, Aax diminishes owing to the equivalent contribution of three-hold t2g orbitals to the spin susceptibility. The orbital mixing is also significant in K2V8O16 having a small Aax/Aiso ∼ 0.1, which is expected to have 0.5 - 0.6 for 3dxy1. In LiV204, Aax/Aiso has a large negative value, as expected in the a1g orbital. The result suggests the presence of the localized spin hidden in the itinerancy, giving the high-entropy state of LiV2O4 at low temperatures.