Dynamic generation of magnon mass in a two-sublattice magnetic chain

The role of quantum effects in an isotropic ferromagnetic chain at zero temperature is discussed. For integral values of (S1 + S2), the low-energy properties of the system in the limit of large but finite spins can be described by the two-dimensional 0(3) σ-model of the field theory with a topological angle θ = 0. For a system with integral values of (S1 + S2), solutions with a nontrivial topology (“instantons”) are derived. The long-range effect of instantons on the behavior of spin correlation functions is considered.