Magnetic behavior of manganese chloride on Kagome and honeycomb lattices

The magnetic properties of transparent pink Na₂Mn₃Cl₈ and NaMnCl₃ are presented. For both phases, the effective magnetic moments are large, while the Curie-Weiss thetas are below 10 K. The compounds crystallize in the trigonal R-3m and R-3 space groups, respectively. A Kagome plane of Mn²⁺ octahedrally coordinated to Cl⁻ is found in Na₂Mn₃Cl₈ and the material has no apparent magnetic ordering above 1.8 K, while the octahedrally coordinated, honeycomb network of Mn²⁺ in NaMnCl₃ orders antiferromagnetically at 6.3 ± 0.2 K. The heat capacity of NaMnCl₃ has one transition, consistent with the susceptibility, while Na₂Mn₃Cl₈ exhibits a more complex heat capacity with two peaks, at 0.6 K and 1.4 K. A third, broad peak near 6.2 K in the heat capacity of Na₂Mn₃Cl₈ is problematic but may be due to the intergrowth of NaMnCl₃ domains.