Ferromagnetism in a hard-core boson model A. Fledderjohann, A. Langari, E. Müller-Hartmann and K.-H. Mütter Eur. Phys. J. B, 43 4 (2005) 471-478 Published online: 30 March 2005 DOI: 10.1140/epjb/e2005-00080-0