Magnetic and structural studies of the Verwey transition in Fe3−δO4 nanoparticles

Stoichiometric and cation-deficient magnetite Fe3−δO4 and γ-Fe2O3 particles have been prepared by the chemical method followed by heat treatments. The magnetic and structural properties were studied using neutron diffraction, magnetic measurements, and Mössbauer spectroscopy. Charge ordering of Fe3+ and Fe2+ and lattice distortion are not observed below the Verwey transition temperature in the stoichiometric and cation-deficient magnetite. It is found that the lattice parameter and the Verwey transition temperature decrease as the cation vacancy increases. The Verwey transition almost disappears in the Fe3−δO4 sample with δ=0.066. Mössbauer spectra show that the ratio of Fe3+/Fe2.5+ in stoichiometric magnetite can be modified by heat treatment. The Fe vacancies on the B sites change the nature of the Verwey transition. No cation vacancy ordering is observed for γ-Fe2O3, due to the small amount of cation vacancies in the compound.