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We report here a novel synthetic method to prepare monodisperse air-stable FeCo nanoparticles with average sizes of 8, 12 and 20 nm. CoFe2O4 nanoparticles of different sizes were first synthesized by a chemical solution method. The as-synthesized CoFe2O4 nanoparticles were then mixed with ball-milled NaCl powders and heated to 400–500 ° C in forming gas (Ar 93%+H2 7%). The salt powder worked as a separating medium that prevents the CoFe2O4 nanoparticles from agglomerating during the heat treatment while the forming gas reduces the CoFe2O4 nanoparticles to FeCo nanoparticles. Monodisperse FeCo nanoparticles were recovered by dissolving the NaCl in water and subsequently washing with ethanol and acetone. Structural analyses confirmed that FeCo nanoparticles retained the same size as their oxide precursors. The size of the FeCo nanoparticles can be well tuned by controlling the size of the CoFe2O4 nanoparticles. The saturation magnetization of FeCo nanoparticles is size dependent and increases with size.

FePt nanorods and nanowires have been synthesized by the reduction of Pt(acac)(2) and the thermal decomposition of Fe(CO)(5) in the presence of solvents/surfactants by simply controlling the sequence of addition of surfactants. The as-synthesized FePt nanorods and nanowires have a face centered cubic structure with average diameter of 3 nm. Length of nanorods and nanowires can be adjusted in the range of 15-150 nm by varying reaction parameters. Nanocrystalline L1(0) FePt phase with coercivity up to 24 kOe was obtained after heat treatments.

Ferromagnetic FeCo nanocrystals with high coercivity have been synthesized using a reductive decomposition method. The sizes and shapes of the nanocrystals were found to be dependent on reaction parameters such as the surfactant ratio, the precursor concentration and the heating rate. Synthesized nanocrystals have a body-centered cubic crystal structure for both particles and nanowires and the (110) crystalline direction is along the long axis of the nanowires. The coercivity and magnetization of the FeCo nanocrystals are found to be dependent on morphology. Nanowires of Fe60Co40 with saturation magnetization of 92 emu g(-1) and coercive force of 1.2 kOe have been obtained in this study.

Hard magnetic nanoparticles based on the Sm(2)Co(17) and SmCo(5) systems have been successfully produced using a surfactant-assisted ball milling technique. A size-selection process has been developed to obtain nanoparticles of different sizes with narrow size distribution. Significant room-temperature coercivity up to 3.1 kOe has been achieved with the Sm(2)Co(17)-based nanoparticles of an average size of 23 nm. It has been found that surfactants play multifold roles in the processing.