Low-dimensional spin S = 1/2 system at the quantum critical limit: Na2V3O7.

We report the results of measurements of the dc susceptibility and the 23Na-NMR response of Na2V3O7, a recently synthesized, nonmetallic low dimensional spin system. Our results indicate that, upon reducing the temperature to below 100 K, the V4+ moments are gradually quenched, leaving only one moment out of nine active. The NMR data reveal a phase transition at very low temperatures. With decreasing applied field H, the critical temperature shifts towards T=0 K, suggesting that Na2V3O7 may be regarded as an insulator reaching a quantum critical point at H=0.

LiVGe2O6, an anomalous quasi-1D, S = 1 system, as revealed by NMR

We report the results of 7Li nuclear magnetic resonance (NMR) studies of LiVGe2O6, a quasi-one-dimensional spin S = 1 model system, at low temperatures. Our data, including NMR spectra and the temperature dependence of the spin-lattice relaxation rate T-11, indicate that a first-order phase transition occurs at T(c) approximately 23 K. The NMR response of LiVGe2O6 below T(c) suggests that the ordered phase is antiferromagnetic and has unusual features. Possible reasons for this unexpected behavior are discussed.