CATION DISTRIBUTION IN NATURAL FERRITES

Mossbauer spectra of jacobsite have been recorded at temperatures of 4 .2, 125, 180, 240 and 300 K and with an external magnetic field of 60 kOe applied parallel to the incident radiation at 4.2 K. The results s how the presence of two different magnetic hyperfine interactions asso ciated with the iron nuclei. Spectra of samples in external magnetic f ields indicate the same sign for the magnetic hyperfine interactions, implying that both iron ions occupy only the octahedral sublattice. Th ese results are compared with data from synthetic stoichiometry mangan ese ferrite, and a model of cation distribution, assuming the existenc e of vacancies, is proposed. According to this model, die mineral jaco bsite is rich in manganese compared with stoichiometric MnFe2O4 ferrit e.