Magnon dispersion and thermodynamics in CsNiF3 - art. no. 224406

We present an accurate transfer matrix renormalization group calculation of the thermodynamics in a quantum spin-1 planar ferromagnetic chain. We also calculate the field dependence of the magnon gap and confirm the accuracy of the magnon dispersion derived earlier through a 1/n expansion. We are th us able to examine the validity of a number of previous calculations and fu rther analyze a wide range of experiments on CsNiF3 concerning the magnon d ispersion, magnetization, susceptibility, and specific hear. Although it is not possible to account for all data with a single set of parameters, the overall qualitative agreement is good and the remaining discrepancies may r eflect a departure from ideal quasi-one-dimensional model behavior. Finally , we present some indirect evidence to the effect that the popular interpre tation of the excess specific heat in terms of sine-Gordon solitons may not be appropriate.