Magnetism of pure iron jarosites

Stoichiometrically pure jarosites of the formula AFe(3)(OH)(6)(SO4)(2) with A=Na+, K+, Rb+, and NH4+ have been afforded by a newly developed redox-based, hydrothermal method. The jarosites exhibit an intralayer antiferromagnetic exchange interaction (-829 K<-812 K) and transition temperatures for long-range order (LRO) (61 K<65 K) that are essentially insensitive to the size of the A(+) ion. A cusp at T-N in the ac susceptibility curve is frequency independent. The origin of LRO is consistent with coupling of jarosite layers exhibiting a net magnetization, which arises from an anisotropy developed, most likely, from the Dzyaloshinsky-Moriya (DM) interaction. A canted intralayer spin structure, which is a consequence of the DM interaction, is signified by a remanent magnetization (similar to 53 K