EXCHANGE INTEGRALS OF VANADATES AS REVEALED BY MAGNETIC-SUSCEPTIBILITY MEASUREMENTS OF NAV2O5

In order to get information on the exchange integrals in vanadates hav ing V4+ ions in a square pyramid geometry, like CaV4O9, we have perfor med measurements of the magnetic susceptibility of a one-dimensional m ember of the family, NaV2O5, whose spin dynamics is controlled by a si ngle exchange integral J between corner-sharing VO5 square pyramids. T he high-temperature part is typical of spin-1/2 chains with a nearest- neighbor antiferromagnetic exchange integral J of 529 K. Under the rea sonable assumption that the exchange between corner-sharing VO5 square pyramids arises mainly from superexchange through O 2p orbitals in al l vanadates, this result indicates that the next-nearest-neighbor exch ange integrals in CaV4O9 have to be larger than 440 and 275 K for inte r- and intraplaquette bonds, respectively.