Synthesis and reactivity of nanophase ferrites in reverse micellar solutions

Self assembly preparative techniques in confined media that lead to magnetic materials with nanometer dimensions are described Synthesis of nanoparticles using the restricted environments offered by surfactant systems such as wafer-in-oil microemulsions (reverse micelles) provide excellent control over particle size, infer-particle spacing, and particle shape. These environments have been used in the synthesis of gamma-Fe2O3, Fe3O4, MnFe2O4, and CoFe2O4 with particle sizes ranging from 10-20 nm. The controlled environment of the reverse micelle also allows sequential synthesis which can produce a core-shell type structure, for example Fe3O4 nanoparticles with MnO coatings. Lyotropic liquid crystal media also offer template effects for the synthesis of magnetic nanostructures. The nanoscale ordering of magnetic particles when synthesized in lyotropic liquid crystal gels is characterized. The structures, theory and modeling concepts, and novel physical properties of these materials are discussed with emphasis given to the differences between course and fine grained magnetic materials. (C) 1999 Acta Metallurgica Inc.