Preparation and magnetic properties of ultrafine particles of Fe-Ni alloys

Ultrafine particles (UFP) of six kinds of Fe-Ni alloys were synthesized by the method of hydrogen plasma reaction. The prepared UFP samples were examined by X-ray diffraction, electron transmission microscopy and magnetic measurement. The spherical Fe-Ni UFP alloys with a mean particle size less than 35 nm can be prepared with a production rate much higher than by conventional methods. The phase constitution of UFP alloys is different from the equilibrium phase diagram owing to rapid condensation of evaporated metal gases. Although the magnetization for the UFP alloys has almost the same temperature dependence as that of the bulk alloys, the saturation magnetization remarkably decreases as the bulk alloys change into the UFP alloys.