Characterizations of Iron Particles Reduced from Iron Oxide Nanoparticles Under Hydrogen Atmosphere

Submicron iron particles were obtained by the reduction of co-precipitated superparamagnetic iron oxide nanoparticles under hydrogen atmosphere. The reduction was carried out at the temperatures ranging from 200 to 1000 °C. The magnetic properties were investigated in accordance with the structural properties. According to the X-ray diffraction patterns, the increase of crystallization was followed by the conversion from iron oxide to iron and also the particle size increased as the reduction temperature increased. Morphology observed by transmission electron microscope showed that the particles were individually seen at low temperatures; however, they stacked together and became larger at high temperatures. Magnetic measurements with a vibrating sample magnetometer disclosed that the saturation magnetization steadily increased with increasing temperature and almost stabilized at 800 °C. Highest saturation magnetization obtained by the reduction process is ～211 emu/g, which is close to that of bulk iron. It is disclosed that, at all temperatures, saturation magnetizations obtained from magnetic measurements were found to be compatible with the structural changes caused by reduction temperature.