The dc magnetron co-sputtering technique was used in fabricating amorphous carbon films containing magnetic Fe3C nanograins. A composite target of a 2-in.-diam graphite disk plus several pieces of iron rods, 2 mm in diameter and 4 mm in length, were used. The films containing pure Fe3C grains could be obtained only in proper sputtering conditions. Films containing only grains of Fe3C phase were subjected to postdeposition annealing at temperatures of 250 to 600 °C for 60 and 90 min, respectively. Auger electron spectroscopy was used to determine the atomic concentration and its fluctuations. The microstructure and phases of grains were determined by high-resolution transmission electron microscopy (HRTEM) and selected area diffraction patterns. Very good crystallinity appeared at Ta≥250 °C. From the HRTEM image, lattice spacings of 6.7 Å—corresponding to Fe3C (001) planes—and 4.3 Å—corresponding to Fe3C (100) planes—were observed. Higher annealing temperature and larger annealing time caused an increase of grain size. The largest grain (18 nm) was obtained at Ta=550 °C. © 2003 American Institute of Physics.