Inelastic neutron scattering has been used to study the magnetic excitation spectrum of Co${\mathrm{Cl}}_2$·2${\mathrm{D}}_2$O in the antiferromagnetically ordered state. The results are analyzed in terms of a model of weakly interacting chains. The dominating interaction is the ferromagnetic Ising coupling along the chains although a comparison to optical studies shows that the Heisenberg nature of the interaction is larger than expected. The transverse anisotropy is found to be confined to relatively small wave vectors indicating that the responsible mechanism has long range in real space. The bound-state magnon branches were not observed.

• Received 2 June 1975

DOI:https://doi.org/10.1103/PhysRevB.12.5190