On the nature of the magnetic transition in a Mott insulator M. Fleck, A. I. Lichtenstein, M. G. Zacher, W. Hanke and A. M. Oleś Eur. Phys. J. B, 37 4 (2004) 439-446 Published online: 09 April 2004 DOI: 10.1140/epjb/e2004-00079-y