Magnetic properties of NaV2O5, a one-dimensional spin 1/2 Heisenberg system with finite chains

We have performed measurements of the magnetic susceptibility of NaV2O5 between 2 and 400 K. The high temperature part is typical of spin 1/2 chains with a nearest–neighbour antiferromagnetic exchange integral of 530 K. We develop a model for the susceptibility of a system with finite chains to account for the low temperature part of the data, which cannot be fitted by a standard Curie-Weiss term. These results suggest that the next nearest–neighbour exchange integral J2 in CaV4O9 should be of the order of 500 K because, like J in NaV2O5, it corresponds to corner sharing VO5 pyramids. PACS Nos : 71.10.+x,75.10.-b,71.30.+h,72.15.Nj