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Concept
Iron oxide nanoparticle
Summary
Iron oxide nanoparticles are iron oxide particles with diameters between about 1 and 100 nanometers. The two main forms are composed of magnetite () and its oxidized form maghemite (γ-). They have attracted extensive interest due to their superparamagnetic properties and their potential applications in many fields (although cobalt and nickel are also highly magnetic materials, they are toxic and easily oxidized) including molecular imaging.
Applications of iron oxide nanoparticles include terabit magnetic storage devices, catalysis, sensors, superparamagnetic relaxometry, high-sensitivity biomolecular magnetic resonance imaging, magnetic particle imaging, magnetic fluid hyperthermia, separation of biomolecules, and targeted drug and gene delivery 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. They have been used in formulations for supplementation.
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 oxygen ions, 21 Fe3+ ions and 2 vacancies. The cations are distributed randomly over the 8 tetrahedral and 16 octahedral sites.
Due to its 4 unpaired electrons in 3d shell, an iron atom has a strong magnetic moment. Ions Fe2+ have also 4 unpaired electrons in 3d shell and Fe3+ have 5 unpaired electrons in 3d shell. Therefore, when crystals are formed from iron atoms or ions Fe2+ and Fe3+ they can be in ferromagnetic, antiferromagnetic, or ferrimagnetic states.
In the paramagnetic state, the individual atomic magnetic moments are randomly oriented, and the substance has a zero net magnetic moment if there is no magnetic field.
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