Highly dispersed ethanol suspensions of spindle-type Fe-Co particles were obtained by the addition of oleic acid with applying ultrasonication. By using this suspension, spindle-type Fe-Co nanoparticles were coated by a uniform silica layer without agglomeration by a sol gel method, in which the total surface area of core Fe-Co nanoparticles and the reaction rate of TEOS were fully controlled. The silica-coated Fe-Co nanoparticles were annealed at 773K in nitrogen-4 % hydrogen mixture gas to reduce surface oxide layer of Fe-Co nanopartilces. The silica-coating densified by the heat treatment led to the substantial improvement of the oxidation-resistant property.
