The magnetic and morphological properties of fine Fe particles have been studied. Ultrafine particles of Fe were prepared using a vapor deposition technique under an argon atmosphere. The argon pressure was varied from 0.5 to 8 Torr during evaporation, and samples with a median diameter in the range 50–200 Å were obtained having a log-normal distribution. The dependence of magnetic properties on particle size and temperature (10 K<T<300 K) were studied using superconducting-quantum-interference-device magnetometry and Mössbauer spectroscopy. Samples with particle diameter below 90 Å showed a superparamagnetic behavior below room temperature. The saturation magnetization of the particles varied from 25 to 190 emu/g, with the higher values corresponding to larger particles. For these larger particles, a coercivity of 1.05 kOe was obtained at room temperature. The magnetic and structural data suggested a core-shell type of structure, where the core consists of metallic Fe and the shell is composed of Fe oxides.

• Received 16 December 1991

DOI:https://doi.org/10.1103/PhysRevB.45.9778