Evidence for a frustrated square lattice with ferromagnetic nearest-neighbor interaction in the new compound Pb2VO(PO4)2

We present the magnetic susceptibility of a new frustrated square lattice system, Pb2VO(PO4)(2), and compare it with that measured on our new samples of Li2VOSiO4 and Li2VOGeO4, the only known examples of such magnetic lattice. The analysis of the data using high-temperature series expansion gives a ferromagnetic nearest-neighbor exchange J(1) similar or equal to - 6 K and an antiferromagnetic next-nearest-neighbor exchange J(2) similar or equal to 9.8 K for Pb2VO(PO4)(2). (C) 2003 Elsevier B.V. All rights reserved.