Thermodynamics and Correlation Functions of Non-Linear Excitations in the Easy-Plane Ferromagnetic Chain

Abstract

The easy-plane ferromagnetic chain with an in-plane symmetry-breaking magnetic field defined by the Hamiltonian

$$H' = - J\sum\limits_n {{{\vec S}_n}} {\vec S_{n + 1}} + A\sum\limits_n {{{\left( {S_n^x} \right)}^2}} - g{\mu _B}{H_O}\sum\limits_n {S_n^z} $$

(1)

is generally believed [1] to describe the excitation spectrum of the magnetic salt CsNiF₃. Owing to the fact that the model (1) in the classical long wave-length limit besides the usual linear extended spin wave spectrum also supports non-linear localized finite-energy domain wall or soliton excitations, this system has attracted much attention both from an experimental and a theoretical point of view.