Magnons in the Linear-Chain Antiferromagnet CsMn<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cl</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>·2<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">D</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>O

This paper reports the first neutron scattering measurements on spin waves in a linear-chain antiferromagnet. Measurements were made on CsMn${\mathrm{Cl}}_{3}$\ifmmode\cdot\else\textperiodcentered\fi{}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, ${J}_{1}=\ensuremath{-}0.304\ifmmode\pm\else\textpm\fi{}0.003$ meV. The exchange parameters in the $b$ and $c$ directions were measured in the combinative form ${J}_{2}+{J}_{3}=\ensuremath{-}0.0021\ifmmode\pm\else\textpm\fi{}0.0004$ meV. Short-wavelength excitations along the chain direction persist even at $2{T}_{N}$.

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