Microstructure and magnetic properties of Fe(C) and Fe(O) nanoparticles

Both Fe(C) and Fe(O) nanoparticles have been successfully synthesized using a modified graphite arc-discharge method. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HREM), and electron diffraction (SAED) analyses indicated that both of these Fe nanoparticles have an average grain size of 15-20 nm and alpha-Fe, gamma-Fe, and Fe3C phases are clearly identified in those Fe(C) particles, while an alpha-Fe and oxide layer (Fe3O4) are revealed in these Fe(O) particles. Mossbauer spectra and hyperfine magnetic fields at room temperature (RT) further confirm their distinct nanophases. At RT, the assemblies of Fe(O) nanoparticles exhibit ferromagnetic properties due to magnetocrystalline anisotropy effects. However, modified superparamagnetic relaxation is observed in the assemblies of Fe(C) nanoparticles.