The compound ${\mathrm{Rb}}_2$Mn${\mathrm{Cl}}_4$ was prepared by two different methods. Neutron diffraction did not reveal any difference in the crystallographic structure and the Néel temperature ($T_{\mathrm{N}}\sim 57$°K) of the samples of the two preparations. The samples did, however, exhibit at $T<\mathrm{}{T}_{\mathrm{N}}$ two distinctly different magnetic structures. It is argued that the appearence of these magnetic polytypes is related to the two-dimensional magnetic behavior of this compound and could in general be expected to occur in compounds exhibiting this behavior.

• Received 1 September 1970

DOI:https://doi.org/10.1103/PhysRevLett.25.1713