Neutron Diffraction and the Magnetic Structure of TlMnCl3

Abstract

Neutron-diffraction and magnetic-susceptibility measurements show that TlMn${\mathrm{Cl}}_{3}$ is an anti-ferromagnet of type $G$ with ${T}_{N}=118$ \ifmmode^\circ\else\textdegree\fi{}K. A transition to weak ferromagnetism is observed at about 108 \ifmmode^\circ\else\textdegree\fi{}K. Reflections in the neutron-diffraction pattern at 330 \ifmmode^\circ\else\textdegree\fi{}K correspond to the undistorted cubic perovskite with ${a}_{0}=5.02$ \AA{}. As temperature is lowered below 330 \ifmmode^\circ\else\textdegree\fi{}K, superlattice lines appear in the neutron-diffraction pattern. An analysis of these lines, assuming the symmetry $\mathrm{Pbnm}$, indicated that the lines are due to a distortion of the ${\mathrm{Cl}}^{\ensuremath{-}}$ octahedra.