Ferromagnetic Nanoparticles: Synthesis, Processing, and Characterization

Ferromagnetic nanoparticles are building blocks of future high density recording media and high performance permanent magnets. However, it is very challenging to produce nanoparticles with ferromagnetism at room temperature. The author describes recent progress in preparing ferromagnetic nanoparticles. Ferromagnetic nanoparticles can be used as building blocks for advanced bulk and thin fi lm magnets, and can also be applied in data storage and biomedical technologies. However, most ferromagnetic particles lose their hysteresis at room temperature when their size is reduced to nanoscale. The exceptions are a few materials such as FePt and SmCo compounds with extremely high magnetocrystalline anisotropy that can hold a permanent magnetic moment at room temperature in particles of several nanometers. By applying newly developed “salt-matrix annealing” and “surfactant-assisted milling” techniques, monodisperse ferromagnetic FePt, SmCo, and NdFeB based nanoparticles have been successfully synthesized. These fi rst-ever-available nanoparticles display various ferromagnetic properties at room temperature, which are found to be strongly size dependent.