Bound-magnon dominance of the magnetic susceptibility of the one-dimensional HeisenbergS=1/2 ferromagnet cyclohexylammonium trichlorocuprate (II)

In order to compare linear spin-wave theory with the effects of nonlinear excitations in spin-1/2 Ising-Heisenberg ferromagnetic chains, we have studied the differential susceptibility of (${\mathrm{C}}_6$ ${\mathrm{H}}_{11}$ ${\mathrm{NH}}_3$)${\mathrm{CuCl}}_3$ in the region 4.2 K<T<40 K, in fields of 0, 1, 2, and 3 T. The data are analyzed in terms of linear spin-wave theory and a nonlinear theory which includes bound-magnon effects. Our analysis shows that linear spin-wave theory cannot describe the data, and that the susceptibility is dominated by the bound-magnon contribution. The correspondence between bound magnons and solitons is discussed.