Abstract

Nanostructured alpha-Fe2O3 powders were prepared by high-energy ball milling. The milling process spans grinding times from 30 min to 24 h. The as-milled samples were characterized by means of Fe-57 Mossbauer spectrometry, Rietveld analysis of X-ray diffraction data and particle size analysis. The obtained results evidence the presence of disordered hematite characterized by a hyperfine field distribution with a well-behaved dependence on the mean crystallite size for which the mean hyperfine field decreases asymptotically as the grain size decreases. A new relationship is proposed in order to describe such behavior. Finally the presence of superparamagnetic grains, the occurrence of a partial topotactic phase transformation into a spinel phase and tool induced contamination are also presented and discussed.