ULTRAFINE PARTICLES OF FE, CO, AND NI FERROMAGNETIC METALS

Fe, Co, and Ni ultrafine particles (UFP) were prepared by a gas evaporation method in an inert atmosphere. The different preparing conditions of the Fe, Co, and Ni UFP included inert gas pressures and kinds were investigated by means of x-ray diffraction, transmission electron microscopy (TEM), and magnetic measurements with low or high temperatures. The experimental results show that coercivities H(c) of the Fe, Co, and Ni UFP, depending on particle sizes, obey a single-domain theory. The maximum H(c) was 450, 1000, and 1500 Oe, respectively, for Ni (310 angstrom), Fe (210 angstrom), and Co (200 angstrom) at room temperature. The coercivities came up to high in the low temperatures. The saturation magnetizations M(s) of the Fe, Co, and Ni UFP decreased with small particle sizes. A face-centered structure of Co UFP (200-300 angstrom) was confirmed by x-ray diffraction. Some Fe UFP in the shape of balls (200-400 angstrom) observed in the TEM may be an amorphous structure.