Iron oxide nanoparticles

Iron oxide nanoparticles are iron oxide particles with diameters between about 1 and 100 nanometers. The two main forms are magnetite (Fe₃O₄) and its oxidized form maghemite (γ-Fe₂O₃). They have attracted extensive interest due to their superparamagnetic properties and their potential applications in many fields (although Co and Ni are also highly magnetic materials, they are toxic and easily oxidized).

Applications of iron oxide nanoparticles include terabit magnetic storage devices, catalysis, sensors, and high-sensitivity biomolecular magnetic resonance imaging (MRI) for medical diagnosis and therapeutics. These applications require coating of the nanoparticles by agents such as long-chain fatty acids, alkyl-substituted amines and diols.

Magnetite has an inverse spinel structure with oxygen forming a face-centered cubic crystal system. In magnetite, all tetrahedral sites are occupied by Fe3+
and octahedral sites are occupied by both Fe3+
and Fe2+
. Maghemite differs from magnetite in that all or most of the iron is in the trivalent state (Fe3+
) and by the presence of cation vacancies in the octahedral sites. Maghemite has a cubic unit cell in which each cell contains 32 O ions, 21 ¹⁄₃ Fe3+
ions and 2 ²⁄₃ vacancies. The cations are distributed randomly over the 8 tetrahedral and 16 octahedral sites.

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Wikipedia