The spin-s quantum Heisenberg ferromagnetic models in the physical magnon theory

The spin-s quantum Heisenberg ferromagnetic model is investigated in the ph ysical magnon theory. The effect of the extra unphysical magnon states on e very site is completely removed in the magnon Hamiltonian and during approx imation procedure so that the condition <a(i)(daggern)a(i)(n)> = 0(n greate r than or equal to 2s + 1) is rigorously satisfied. The physical multi-appr oximation occupancy <a(i)(daggern) a(i)(n)> (1 less than or equal to n less than or equal to 2s) is proportional to T-3n/2 at low temperature and is e quivalent to 1/(2s + 1) at the Curie temperature. The magnetization not onl y unified but also well-behaved from zero temperature to Curie temperature is obtained in the framework of the magnon theory for the spin-s quantum He isenberg ferromagnetic model. The ill-behaved magnetizations at high temper ature in earlier magnon theories are completely corrected. The relation of magnon (spin wave) theory with spin-operator decoupling theory is clearly u nderstood. (C) 2001 Elsevier Science B.V. All rights reserved.