Long-Range Magnetic Ordering in Iron Jarosites Prepared by Redox-Based Hydrothermal Methods

The iron jarosites, plumbojarosite, Pb0.5Fe3(OH)6(SO4)2, argentojarosite, AgFe3(OH)6(SO4)2, and
thallium jarosite, TlFe3(OH)6(SO4)2, along with the selenate-capped jarosite analogues of potassium, KFe3(OH)6(SeO4)2, and rubidium, RbFe3(OH)6(SeO4)2, have been prepared in their analytically pure forms by
employing redox-based hydrothermal methods. The crystal structures of these materials have been
determined, and all are found to be essentially isostructrual including Pb0.5Fe3(OH)6(SO4)2, which is distinct
from the structure reported for naturally mined samples. All iron jarosites show long-range order (LRO),
signified by a sharp transition temperature, TN, which falls in the narrow temperature range of 61.4 ± 5 K.
The mechanism responsible for this ordering has been established by examining magnetostructural
correlations for the jarosites possessing various interlayer cation and capping groups. We show that all
magnetic properties of jarosites, including LRO, find their origin in the basic magnetic unit, the intralayer
Fe3(μ-OH)3 triangle. Field-dependent magnetization experiments are consistent with the antiferromagnetic
stacking of an out of plane moment developed from spin canting within Fe3(μ-OH)3 triangles. Together
with the previously reported AFe3(OH)6(SO4)2 (A = Na+, K+, Rb+ and NH4+) jarosites, these compounds
provide a framework for probing magnetic ordering in a spin frustrated lattice of the largest series of
isoelectronic and isostructural kagomé systems yet discovered.