Linear Chain Antiferromagnetism in 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">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>O

The magnetic susceptibilities of orthorhombic single crystals of CsMn${\mathrm{Cl}}_{3}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O have been measured along the $a$, $b$, and $c$ axes between 0.35 and 77\ifmmode^\circ\else\textdegree\fi{}K. Above \ensuremath{\sim}9\ifmmode^\circ\else\textdegree\fi{}K, the susceptibility is essentially that of a system of extended weakly interacting chains of spins ($S=\frac{5}{2}$, $g=2.00$) antiferromagnetically coupled by nearest-neighbor Heisenberg exchange interaction. The magnitude of the intrachain interaction has been deduced by comparison with Fisher's classical limiting form of the theory of the Heisenberg chain, with and without corrections for the finite spin of the ${\mathrm{Mn}}^{+\phantom{\rule{0ex}{0ex}}+}$ ion. With such corrections one finds $J=\ensuremath{-}3.00k$. A small uniaxial anisotropy evident at hydrogen temperatures is attributed primarily to single-ion effects. Below \ensuremath{\sim}5\ifmmode^\circ\else\textdegree\fi{}K, interchain interaction apparently causes long-range antiferromagnetic ordering, with the $a$ axis the preferred direction of spin orientation. At 0.35\ifmmode^\circ\else\textdegree\fi{}K an anomalous temperature dependence of uncertain origin is seen.

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