Evidence for Soliton Modes in the One-Dimensional Ferromagnet CsNiF3

Evidence for solitons moving along the ferromagnetic chains in CsNi${\mathrm{F}}_3$ has been obtained by inelastic neutron scattering. As predicted by Mikeska the scattering is found at low $q$, around zero energy. The soliton activation energy, $8m$, is determined via the temperature and field dependence of the intensities ($m$ is the effective mass of the quasiparticle soliton). At $H=5\mathrm{}$ kG we find $\frac{8m}{k_{\mathrm{B}}}=27\mathrm{}$ K in reasonable agreement with the predicted value, as is the energy width at $q=0.1\mathrm{}$.