Spin correlations and exchange in square-lattice frustrated ferromagnets

The J(1)-J(2) model on a square lattice exhibits a rich variety of different forms of magnetic order that depend sensitively on the ratio of exchange constants J(2)/J(1). We use bulk magnetometry and polarized neutron scattering to determine J(1) and J(2) unambiguously for two materials in a new family of vanadium phosphates, Pb2VO(PO4)(2) and SrZnVO(PO4)(2), and we find that they have ferromagnetic J(1). The ordered moment in the collinear antiferromagnetic ground state is reduced, and the diffuse magnetic scattering is enhanced, as the predicted bond-nematic region of the phase diagram is approached. Copyright (C) EPLA, 2009