NMR and dc susceptibility studies of NaVGe2O6

We report the results of measurements of the dc magnetic susceptibility $\ensuremath{\chi}$ and of the $^{23}\mathrm{Na}$ nuclear magnetic resonance (NMR) response of ${\mathrm{NaVGe}}_{2}{\mathrm{O}}_{6}$, a material in which the $\mathrm{V}$ ions form a network of interacting one-dimensional spin $S=1$ chains. The experiments were made at temperatures between 2.5 and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The $\ensuremath{\chi}(T)$ data suggest that the formation of the expected low-temperature Haldane phase is intercepted by an antiferromagnetic phase transition at ${T}_{N}=18\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The transition is also reflected in the $^{23}\mathrm{Na}$ NMR spectra and the corresponding spin-lattice relaxation rate ${T}_{1}^{\phantom{\rule{0.2em}{0ex}}\ensuremath{-}1}(T)$. In the ordered phase, ${T}_{1}^{\phantom{\rule{0.2em}{0ex}}\ensuremath{-}1}(T)$ decreases by orders of magnitude with decreasing temperature, indicating the formation of a gap of the order of $12\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in the magnetic excitation spectrum.