Quantum spin dynamics of the bilayer ferromagnet La1.2Sr1.8Mn2O7 N. Shannon, T. Chatterji, F. Ouchni and P. Thalmeier Eur. Phys. J. B, 27 3 (2002) 287-297 Published online: 06 June 2002 DOI: 10.1140/epjb/e2002-00157-2