Neutron Scattering in the Linear Chain Antiferromagnet CsMnCl3·2H2O

Abstract

Highly unusual magnetic scattering of neutrons has been observed in CsMn${\mathrm{Cl}}_{3}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O (${T}_{N}=4.89$ \ifmmode^\circ\else\textdegree\fi{}K). The scattering in reciprocal space occurs in planes of constant intensity at temperatures as high as $10{T}_{N}$. These planes are perpendicular to the ${a}^{*}$ axis and peak strongly at $h$ odd. This is the first observation of definitive evidence for linear antiferro-magnetic chains. At approximately $2{T}_{N}$, the planes develop an intensity variation with peaks occurring in the vicinity of eventual magnetic Bragg peaks. The nature of the scattering here is indicative of long chains of spins becoming correlated in the remaining two dimensions through weak interchain coupling. The substance thereupon attains a three-dimensional ordering at ${T}_{N}$. The sublattice magnetization below ${T}_{N}$ follows a power-law behavior in the range $0.0005<\frac{({T}_{N}\ensuremath{-}T)}{{T}_{N}}<0.07$ with critical exponent 0.30.