Preparation and characterization of single phase γ-Fe nanopowder from cw CO₂ laser induced pyrolysis of iron pentacarbonyl

Pure γ-Fe particles were prepared from cw CO₂ laser induced pyrolysis of iron pentacarbonyl. The synthesized particles were characterized by means of transmission electron microscopy, X-ray diffraction and vibrating sample magnetometer. The particle size ranged from 30 to 80 nm diameter and showed clear crystal habit of polyhedra. It is found that many planar defects, such as stacking faults and twins occurred in the γ-Fe particles. The reason for the formation of defects is discussed. In addition, annealing experiments of the γ-Fe ultrafine particles were carried out at 100-500°C and magnetic properties of the annealed powder were examined at room temperature. It is indicated that the γ-Fe phase is stable at room temperature and the transformation of γ-Fe to α-Fe starts at above 250°C.