Linear-Chain Antiferromagnetism in [(CH3)4N] [MnCl3]

This paper reports optical and magnetic properties of tetramethyl ammonium manganese trichloride, [${\left(\mathrm{C}{\mathrm{H}}_3\right)}_4$N][Mn${\mathrm{Cl}}_3$]. Magnetically, the system is one of very weakly interacting chains of ${\mathrm{Mn}}^{++}$ ions. Magnetic-susceptibility measurements are given from room temperature to below 1°K and show a possible phase transition at 0.84°K. Theoretical analysis reveals that the system approximates very closely a Heisenberg linear-chain antiferromagnet with interchain interactions many orders of magnitude smaller than intrachain exchange $J$. We find $J=6.3\mathrm{}°$K and a susceptibility maximum at 55°K. The optical spectrum shows certain features that are not easily accounted for by an isolated Mn${\mathrm{Cl}}_6$ cluster, and may contain information concerning the nature of low-temperature dynamics of the Heisenberg linear chain, although no positive identification of magnon sidebands has yet been made.