9 research outputs found
A low-dimensional spin S = 1/2 system at the quantum critical limit: Na2V2O7
We report the results of measurements of the dc-susceptibility and the
23Na-NMR response of Na2V2O7, a recently synthesized, non metallic low
dimensional spin system. Our results indicate that upon reducing the
temperature to below 100 K, the V^{4+} moments are gradually quenched, leaving
only one moment out of 9 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 Na2V2O7 may be regarded as an insulator
reaching a quantum critical point at H = 0.Comment: 4 pages, 5 figure
The nature of the nitrite disorder in Na3ONO2
The nature of the disorder present in Na3ONO2 has been studied
using variable temperature solid state nuclear magnetic
resonance techniques. Using N-15 MAS and static NMR line shape
analysis, the disorder could be unambiguously ascribed to a
reorientational motion of the nitrite anion. A detailed
analysis of the line shapes revealed that at room temperature
the dynamic is characterized by a rapid pseudo-isotropic
reorientation of the NO2- group, in which the nitrogen atom
occupies the six possible orientations with equal probability.
The exchange process is not characterized by a continuous
decrease in the exchange frequency with decreasing temperature,
but has rather to be described by a dynamic order process. Upon
decreasing the temperature, one of the six possible split
positions for the nitrogen atom becomes increasingly favorable,
leading to a preferential occupation of the two nitrite
orientations related to this split position. Thus, the
transition from H-Na3ONO2 (isotropically reorienting nitrite
ions) to the M-phase is continuous and characterized by the
continuous order process of the nitrite ion