T. Michoel, A. Verbeure
Mathematical Structure of Magnons in Quantum Ferromagnets
(25K, LaTeX 2e)

ABSTRACT.  We provide the mathematical structure and a simple, transparent and 
rigorous derivation of the magnons as elementary quasi-particle 
excitations at low temperatures and in the infinite spin limit for a 
large class of Heisenberg ferromagnets. The magnon canonical variables 
are obtained as fluctuation operators in the infinite spin limit. Their 
quantum character is governed by the size of the magnetization.