Hyperfine interactions and magnetic properties of nanosized powders of magnetite

The fine powder of magnetite Fe₃O₄ was obtained by precipitation of aqueous solutions of chemically pure Mohr's salt Fe(NH₄)₂(SO₄)₂·6H₂O and FeCl₃ using concentrated NH₄OH. The fine powders with the particle size from 5 to 25 nm were obtained. Some portions of powders were subjected to heat treatment in air at temperatures of 473, 573 and 673 K. This annealing leads to the formation of γ-Fe₂O₃. The parameters of hyperfine interactions for these ions in the crystal structure of Fe₃O₄ and γ-Fe₂O₃ by the nuclear gamma-resonance method (NGR) were obtained and difference in occupations of iron ions in octa- and tetra-sublattice compared to stoichiometric magnetite was revealed.