EPL, 88 (2009) 57005
DOI: 10.1209/0295-5075/88/57005

Spin correlations and exchange in square-lattice frustrated ferromagnets

M. Skoulatos¹, J. P. Goff², C. Geibel³, E. E. Kaul³, R. Nath³, N. Shannon⁴, B. Schmidt³, A. P. Murani⁵, P. P. Deen⁵, M. Enderle⁵ and A. R. Wildes<sup>5

1</sup>   Helmholtz Centre Berlin for Materials and Energy - Hahn-Meitner-Platz 1, 14109 Berlin, Germany, EU
²   Department of Physics, Royal Holloway, University of London - Egham, Surrey TW20 0EX, UK, EU
³   Max-Planck Institute for Chemical Physics of Solids - Nöthnitzer Str. 40, Dresden 01187, Germany, EU
⁴   H.H. Wills Physics Laboratory, University of Bristol - Bristol BS8 1TL, UK, EU
⁵   Institut Laue-Langevin - BP 156X, 38042 Grenoble Cedex, France, EU

markos.skoulatos@helmholtz-berlin.de

received 14 October 2009; accepted in final form 12 November 2009; published December 2009
published online 11 December 2009

Abstract
The J₁-J₂ model on a square lattice exhibits a rich variety of different forms of magnetic order that depend sensitively on the ratio of exchange constants J₂/J₁. We use bulk magnetometry and polarized neutron scattering to determine J₁ and J₂ 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 J₁. 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.

PACS
75.30.Et - Exchange and superexchange interactions.
75.40.Cx - Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.).
75.40.Gb - Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.).

© EPLA 2009