Site-selective NMR in the quasi-1D conductor ββ-Sr0.33V2O5Sr0.33V2O5

We report 51V NMR experiments in the metallic phase of the quasi-one-dimensional (1D) conductor ββ-Sr0.33V2O5Sr0.33V2O5. The Knight shift and the quadrupole splitting of all six vanadium sites were determined as a function of the direction of magnetic field perpendicular to the conducting bb-axis. Magnetic properties of the three 1D structural units are remarkably heterogeneous. In particular, the V2 ladder unit shows pronounced charge disproportionation among the two (V2a and V2b) sites. At one of these sites, the absolute value of the Knight shift and 1/(T1T)1/(T1T) increase steeply with decreasing temperature, suggesting development of ferromagnetic correlation.