Magnons in the Linear-Chain Antiferromagnet CsMnCl3·2D2O

This paper reports the first neutron scattering measurements on spin waves in a linear-chain antiferromagnet. Measurements were made on CsMn${\mathrm{Cl}}_3$·2${\mathrm{D}}_2$O and clearly indicate a large directional anisotropy of the spin coupling. The dominant exchange occurs along chains extending in the $a$ direction, $J_1=-0.304\mathrm{}\pm 0.003$ meV. The exchange parameters in the $b$ and $c$ directions were measured in the combinative form $J_2+J_3=-0.0021\mathrm{}\pm 0.0004$ meV. Short-wavelength excitations along the chain direction persist even at $2T_N$.