Magnetic Nanomaterials: Conventional Synthesis and Properties
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Nanophased magnetic materials have wide applications in magnetic recording device, ferrofluids, and biomedical science. Nanoscale particles are considered to have a size range from 1 to 100 nm. Particles within this size range usually have hybrid properties different from those of the bulk solid or the molecular/atomic species. The unique properties of nanoscale particles can be attributed to two basic phenomena. The first is that the number of atoms at the surface and/or interface in these materials is comparable to that of atoms located in the crystal lattice. Therefore the chemical and physical properties, which are normally determined by the structure of the bulk lattice, become increasingly dependent upon the atoms at the surface and interface. The high number of atoms on the surfaces of nanoparticles form a layer of “damaged” lattice with a higher energy state; therefore these particles are highly unstable and more reactive. The second phenomenon is the “quantum-size effect” or “quantum confinement effect.” When particles approach the nanometer-size range, their electronic and photonic properties can be significantly modified as a result of the absence of a few atoms in the lattice and the regional relaxation of the lattice structure.
The small size and rich surface/interface structure of magnetic nanomaterials can lead to properties quite different from those of the bulk. Studies on magnetic nanomaterials will not only provide information about the structure–property relations of magnetic nanomaterials but also help generating new ideas and technologies for the fabrication and application of these materials. The first part of this review will describe common fabrication techniques for magnetic nanomaterials. The second part will give a brief introduction to the theoretical aspects of fine particle magnetism; experimental results on some of these topics will also be discussed.