Direct evidence for cobalt substitution effects in magnetite

We synthesized Fe3−xCoxO4 (x=0–0.6) using the hydrothermal method in order to demonstrate substitutional effects on the hyperfine magnetic fields and populations of the tetrahedral (A) and octahedral (B) sites of magnetite. Our Mössbauer spectroscopy results provided direct evidence for the presence of the Co substitution in the B sublattice, which was found to be accompanied by a systematic increase of the hyperfine magnetic field at these sites. The mechanism we propose relies on the substitution of Fe2+ by Co2+ in the B sublattice and is supported by the observed dependence of the populations of the (A) and (B) sites on the content x of cobalt substitution. For the particular value x=0.1, we report that the two sublattices of magnetite become equally populated.