Exchange integrals of vanadates as revealed by magnetic-susceptibility measurements ofNaV2O5

In order to get information on the exchange integrals in vanadates having ${\mathrm{V}}^{4+}$ ions in a square pyramid geometry, like ${\mathrm{CaV}}_4$ ${\mathrm{O}}_9$, we have performed measurements of the magnetic susceptibility of a one-dimensional member of the family, ${\mathrm{NaV}}_2$ ${\mathrm{O}}_5$, whose spin dynamics is controlled by a single exchange integral J between corner-sharing ${\mathrm{VO}}_5$ 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 ${\mathrm{VO}}_5$ square pyramids arises mainly from superexchange through O 2p orbitals in all vanadates, this result indicates that the next-nearest-neighbor exchange integrals in ${\mathrm{CaV}}_4$ ${\mathrm{O}}_9$ have to be larger than 440 and 275 K for inter- and intraplaquette bonds, respectively. © 1996 The American Physical Society.