SPIN-WAVE-THEORY ANALYTIC SOLUTION OF A HEISENBERG-MODEL WITH LONG-RANGE INTERACTIONS ON A BETHE LATTICE

An analytic solution for the Heisenberg Hamiltonian with arbitrarily l ong-range, ferromagnetic and/or antiferromagnetic, interactions on a B ethe lattice is obtained in the semiclassical approximation (S --> inf inity). The density of states of the excitations is evaluated in the o ne-spin-wave approximation. The stability of a general helical ground state configuration, against variations in the magnitude and sign of t he long-range interactions, is investigated for several illustrative e xamples, generating a wealth of sharp and smooth parametric transition s.