Abstract
We studied magnetic properties of powder samples of Susceptibility above the antiferromagnetic (AF) transition temperature agrees with susceptibility obtained from the one-dimensional Heisenberg model with competing AF interactions. Since the estimated ratio (0.27–0.31) between nearest-neighbor and next-nearest-neighbor AF exchange interactions is close to a critical value (0.24–0.30) which determines whether a spin gap exists or not, the spin system in is probably located near a boundary between spin systems with gapless and gapped magnetic excitation. The value of where is the temperature at which the susceptibility is maximum, shows a unique dependence on x. We speculate that a spin gap due to competing AF interactions exists at and that magnetic excitation is gapless at explaining qualitatively the dependence of on x.
- Received 2 July 2003
DOI:https://doi.org/10.1103/PhysRevB.68.214421
©2003 American Physical Society