A comparison of static and dynamic properties of one-dimensional magnets and corresponding sG system

Using numerical transfer-integral and molecular-dynamic calculations, we demonstrate that the mapping of an easy-plane ferromagnet in a field to the sine-Gordon system fails at surprisingly low temperatures. The crucial implication for CsNiF3 is that the central peak observed by Kjems and Steiner at T = 10 K is more likely to be due to multimagnon difference processes, or pulse-soliton features of the nearly isotropic model rather than due to kink or breather solitons.