An Algebraic Realization of Spin-Wave Theory

Abstract

The Heisenberg Hamiltonian of a ferromagnet with Zeeman term is treated by the method of algebraic realization of the spin algebra. The general features of this approach are first analyzed. A detailed calculation with a particular algebraic realization is then carried out by use of two boson operators; one of the operators is interpreted as the observable spin waves and the other as ``spurions'' which carry only spin quantum number without energy. The Bethe-Salpeter integral equation is solved in the long-wavelength region for the bound states of spin waves. A perturbation calculation yields a leading T4 correction to the usual T3/2 behavior of the magnetization.