Moessbauer parameters for ferrihydrites at 4 K

Abstract

The Moessbauer spectra at 4.2K for five ferrihydrites (one natural, four synthetic) have been determined. Two of the samples contained silicon (atomic ratio Si/Fe= 18%, 21%) and one contained aluminium (Al/Fe = 19%). The Moessbauer parameters were calculated from peak positions estimated by a fit of one set of six Lorentzian lines to each spectrum and by judging absorption maxima by eye. Hyperfine magnetic field (H) values were between 50.0 and 50.4 T for pure samples and between 48.3 and 49.2 T for samples containing silicon or aluminium. Variations as small as these, due to impurities, would not prevent ferrihydrite being distinguished from lepidocrocite (H= 46.0 ± 0.5 T for pure, well-crystallized material) in Moessbauer spectra of soil samples at 4.2 K.