Iron Oxide Nanoparticles
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Iron oxide is one of the oldest materials used even in archeological founds, e.g., in Ajanta or in Altamira, as red pigments. Even today, its significance in the pigmental materials is not lost. Since the advent of magnetic recording systems, however, ferromagnetic iron oxides gained its importance quite rapidly. These two important application fields are coupled to gain magnetic or intelligent inks.
There are many chemical species categorized as iron oxides. While hematite (α-Fe2O3), maghemite (γ-Fe2O3), and magnetite (Fe3O4) are, by far, the most important species of pure iron oxides, many hydroxides, such as ferric hydroxide (Fe(OH)3), and oxyhydroxides, such as goethite (α-Fe(O)OH), are also of industrial significance, particularly as precursors of pure or complex oxides. As for the complex iron oxides, ferrites are of particular importance as ferromagnetic materials.
Like many other nanoparticles, those of iron oxides and ferrites are prepared either via wet chemical routes such as colloid chemical or sol-gel methods or by dry processes such as vapor deposition techniques. Usually, nanoparticles are not shaped by conventional granulometrical methods. Instead, they are most frequently arranged to films, so that many preparation methods of thin films are regarded as those for nanoparticles as well. It is often desired to assemble or pattern iron oxide nanoparticles to give magnetic or optomagnetic functions.
This review summarizes the preparation, magnetic properties, and some representative examples for application of the pure and complex iron oxides.