Oxidation characteristics and magnetic properties of iron carbide and iron ultrafine particles

Magnetic Fe3C and alpha-Fe ultrafine particles were prepared by laser-induced pyrolysis of Fe(CO)(5) and C2H4. It is found that after passivation, the Fe3C particles exhibit a high saturation magnetization of 132 emu/g compared to that of the alpha-Fe particle, 95 emu/g. By determining the oxygen content and the present states of oxygen the particles contained, it is found that not only oxygen content of the alpha-Fe particles is much higher than that of the Fe3C particles, but the oxygen is in differnt states for the two ultrafine particles. The oxygen present on the Fe3C particles is primarily in absorbed form, compared to chemically combined oxygen as in the alpha-Fe particles. Thin amorphous carbon layers, formed on the surfaces of the Fe3C particles, inhibit oxidation of the Fe3C and therefore result in higher saturation magnetization achieved by Fe3C particles, relative to the alpha-Fe particles on which no carbon layer was present. (C) 1996 American Institute of Physics.