Abstract
The occurrence of hausmannite with an apparent Curie temperature close to 750 K, instead of 41.8 K was recently described from hydrothermally altered manganese ore from the Kalahari manganese field, South Africa. The unusual magnetic properties were related to the substitution of Fe (super 3+) for Mn in the hausmannite structure. Because of the large differences in the scattering lengths of Fe and Mn, b Fe = 9.94 and b Mn = -3.73 fm, respectively, we performed neutron powder diffraction experiments at 295 and 10 K on natural mineral separates and synthetic compounds to determine the influence of the Fe substitution on the crystal structure and the magnetic properties of the hausmannite. Rietveld refinements of synthetic Fe-rich hausmannite neutron powder diffraction patterns at 295, 60, and 10 K indicate some significant and interesting changes of magnetic properties and crystal structure of hausmannite, which are directly linked to an increasing amount of iron substituting for manganese. The unit-cell parameters of Mn (sub 3-x) Fe x O 4 ?, in particular, illustrate decreasing Jahn-Teller distortion with increasing Fe content, whereas the Curie temperature was found to increase significantly with increasing Fe content. Nevertheless, this study indicates that the presence of Fe-rich hausmannite causes the unusual high-temperature ferrimagnetic behavior in the Kalahari manganese field.
