THE MAGNETIC-HYPERFINE-FIELD DISTRIBUTION IN ALUMINOUS HEMATITE

Mossbauer spectra of two synthetic aluminium-substituted haematites ha ve been fitted with a model magnetic-hyperfine-field distribution whic h takes the form of a Boltzmann distribution for the z component of th e sublattice magnetization. Good fits were obtained, and the hyperfine -field distribution is attributed to moment fluctuations on a longer t imescale than the measurement time for Fe-57 Mossbauer spectroscopy. T he fit parameters were compared with the predictions of a mean-field m odel for magnetic ordering in a diamagnetically substituted antiferrom agnet.