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

Stoichiometric and cation-deficient magnetite ${\mathrm{Fe}}_{\text{3−δ}}{\mathrm{O}}_4$ and $\mathrm{\gamma -}{\mathrm{Fe}}_2{\mathrm{O}}_3$ 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 ${\mathrm{Fe}}^{\text{3+}}$ and ${\mathrm{Fe}}^{\text{2+}}$ 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 ${\mathrm{Fe}}_{\text{3−δ}}{\mathrm{O}}_4$ sample with δ=0.066. Mössbauer spectra show that the ratio of ${\mathrm{Fe}}^{\text{3+}}/{\mathrm{Fe}}^{\text{2.5+}}$ 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 $\mathrm{\gamma -}{\mathrm{Fe}}_2{\mathrm{O}}_3,$ due to the small amount of cation vacancies in the compound.