Exchange integrals of vanadates as revealed by magnetic-susceptibility measurements of NaV2O5

In order to get information on the exchange integrals in vanadates having V4+ ions in a square pyramid geometry, like CaV4O9, we have performed measurements of the magnetic susceptibility of a one-dimensional member of the family, NaV2O5, whose spin dynamics is controlled by a single exchange integral J between corner-sharing VO5 square pyramids. The high-temperature part is typical of spin-1/2 chains with a nearest-neighbor antiferromagnetic exchange integral J of 529 K. Under the reasonable assumption that the exchange between corner-sharing VO5 square pyramids arises mainly from superexchange through O 2p orbitals in all vanadates, this result indicates that the next-nearest-neighbor exchange integrals in CaV4O9 have to be larger than 440 and 275 K for inter- and intraplaquette bonds, respectively.