Solitons and the excitation spectrum of classical ferromagnetic chains with axial anisotropy

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Abstract
With the use of the molecular-dynamics technique and nonlinear spin-wave theory, we investigate the relevance of envelope solitons in dynamic form factors in classical one-dimensional Heisenberg models with axial anisotropy. We find that magnon bound-state contributions survive in the classical limit. Their main effects are a central peak, a bound-state resonance, and the removal of unphysical singularities. The correspondence between envelope solitons and magnon bound states as obtained by semiclassical quantization provides an interpretation of these effects as soliton features. Comparison with previous results for spin ½ suggests that the structure of the dynamic form factors at finite temperature is essentially independent of the spin value.