Effect of anisotropy on the ground-state magnetic ordering of the spin-half quantum J1 –J2 XXZ model on the square lattice

R. F. Bishop,1,2 P. H. Y. Li,1,2 R. Darradi,3 J. Schulenburg,4 and J. Richter3 1School of Physics and Astronomy, Schuster Building, The University of Manchester, Manchester, M13 9PL, United Kingdom 2School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, Minnesota 55455, USA 3Institut für Theoretische Physik, Universität Magdeburg, P.O. Box 4120, 39016 Magdeburg, Germany 4Universitätsrechenzentrum, Universität Magdeburg, P.O. Box 4120, 39016 Magdeburg, Germany Received 20 May 2008; revised manuscript received 6 July 2008; published 11 August 2008