The structure of iron oxide is based on a cubic inverse single group structure

Comprising a packed array of neighboring cubes, the Fe2+ ions occupy half of the octahedral sites, with Fe3+ cations being split evenly across the unoccupied octahedral and tetrahedral sites. Fe3O4 samples are non-stoichiometric, where the temperature-dependent ferromagnetism originates from the coupling of spins of Fe2+ and Fe3+ electrons in the octahedral sites. Therefore, the octahedral and tetrahedral sites induce the magnetic field, giving it permanent magnetism. Synthetic and natural magnetic crystals adopt opaque jet-black color and metallic luster. The density of Fe3O4 is 5.18 g/cm3, a bit lighter than the reddish-brown Fe3O4. Generally, Fe3O4 magnetite particles exhibit a hardness of 5.5, similar to glass at ambient temperatures. Effective surface areas of magnetite differ based on the preparation method and how certain procedures lead to coarser and finer particles. Nevertheless, common micro-scale particles with diameters of 0.2 µm approximately exhibit higher surface areas.

It should be noted that Magnetite particles are not porous. In the case of solubility, Fe3O4 dissolves much faster than other iron oxides. The melting and boiling points Fe3O4 are as high as 1590 and 2623 °C, respectively, with the fusion heats, vaporization, and decomposition as 138.16 and 298.0, and 605.0 kJ/mole, at elevated temperatures of 2623 °C. As it was discussed earlier, octahedral sites in Fe3O4 contain both ferrous (Fe2+) and ferric (Fe3+) with electrons coordinated with these cations being thermally delocalized, leading to the migration of electrons within the limits of Fe3O4 structure to finally result in high conductivity. The transitional temperature of Fe3O4 causes regular arrangement of ferrous and ferric iron cations in the fabric of octahedral sites. Such an arrangement inhibits electron delocalization when the temperature falls. Additionally, Fe3O4 could be a bit of a deficient metal crystal on octahedral sites. This lack of metallic property leads to n-type p-type magnetite semiconductors. The magnetic properties are particularly dependent on the Fe3O4’s Curie temperature, which was discussed already. At thermal conditions lower than the Curie temperature, the magnetic moments of tetrahedral sites occupied by ferric irons get aligned ferromagnetically.

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