Dynamical correlation functions in a one-dimensional Ising-like antiferromagnetic CsCoCl3: A neutron scattering study

Abstract

Spin dynamics in a one-dimensional (1D) antiferromagnet CsCo${\mathrm{Cl}}_3$ is studied by inelastic neutron scattering. We report the first experimental evidence for a propagative mode of 1D antiferromagnetic domain walls predicted by Villain. Instead of a usual Lorentzian line shape, a characteristic shoulder can be seen in $S_{\mathrm{zz}}(q,\omega )$ near $\omega =0\mathrm{}$ for $q>~\kappa$. This shoulder appears only at elevated temperatures, which indicates that the shoulder intensity corresponds to the number of thermally activated domain walls. The 1D antiferromagnet domain-wall motion can also affect the spin-wave spectrum as shown by theoretical calculation of Ishimura and Shiba. The observed spectrum consists of the excitation continuum of nondegenerate magnon states due to the motion of 1D antiferromagnet domain walls. Using the dispersion formula $\hslash {\omega }_q=2J(1-8\mathrm{}{\epsilon }^2{cos}^{2}qc)$, we evaluate the exchange $2J$ and $\epsilon$ to be 12.75 ± 0.1 meV and 0.14 ± 0.02, respectively. These values can describe both the boundaries of the excitation continuum $2J\pm 4\epsilon J\left|cosqc\right|$ and the shoulder position in $S_{\mathrm{zz}}(q,\omega )$, $4\epsilon J\left|sinqc\right|$, correctly. The asymmetry of the spin-wave line shapes with heavy spectral density towards the lower-energy side, is, however, more enhanced than the theoretical prediction.