Fe–Co and Fe–Ni magnetic fine particles encapsulated by graphite carbon

Magnetic fine particles of Fe–Co and Fe–Ni alloys encapsulated by graphitic carbon (C) were synthesized by annealing Fe2O3,Co3O4, and NiO with carbon powders at 1273 K in nitrogen atmosphere. Saturation magnetizations of the Fe–Co and Fe–Ni particles were 122–150 and 7.8–105Am2∕kg, respectively. X-ray diffraction measurement showed that the Fe–Co was composed of two phases with face-centered-cubic (fcc) and body-centered-cubic phases, while the Fe–Ni was only a fcc phase. Lattice constants of both particles depended on their composition, which suggested that they were alloys. This was confirmed by Mössbauer spectroscopy. Electron microscope images and electron energy loss spectroscope spectra revealed that these particles with diameters of 100–200 nm were encapsulated by C layers with a thickness of several tens of nanometers.