Magnetic properties of ultra-fine iron particles

Ultra-fine iron particles of sizes ranging from 75 to 300 A were prepared by the gas-evaporation method in an argon atmosphere. By controlling the pressure of argon gas, various sizes of iron particles were made. From TEM micrographs, the mean particle size is determined. Magnetic properties of these particles were obtained by a vibrating sample magnetometer. It is considered that an oxidation layer may be formed on the surface of iron particles, when they are exposed to air. Based on this surface effect, most of the observed magnetic behavior, such as temperature dependences of magnetization and coercive force, can be explained. X-ray differential scanning calorimetry measurements were also performed on these particles. (orig.)