Spin Correlations in a One-Dimensional Heisenberg Antiferromagnet

Quasielastic magnetic neutron scattering from the linear-chain antiferromagnet ${\left(\mathrm{C}{\mathrm{D}}_3\right)}_4$NMn${\mathrm{Cl}}_3$ is reported. The system is found to exhibit planes of critical scattering perpendicular to the Mn${\mathrm{Cl}}_3$ chains from >40°K down to 1.1°K. Both the spatial and thermal variation of the scattering can be quantitatively accounted for at all temperatures using Fisher's theory for the classical Heisenberg linear chain.