Structure and Magnetic Properties for Fe-C Films Fabricated in Ar+N2 Plasma

The soft magnetic properties of Fe-C films sputtered in Ar+N2 plasma are examined, and the relations between the effective permeability ¿eff and metallurgical structure, such as grain size and lattice strain, are discussed. Excellent soft magnetic properties, with ¿eff = 1400, were obtained in Fe-1.6 at% C-N films annealed at 300°C, at which temperature the martiensite phase (bet Fe-C) disappeared. From the X-ray diffracted line from the (110) crystal plane of ¿-Fe, it was found that the films consist of fine grains. This fact may suggest that the formation of iron nitride rather than Fe3C by annealing at 300°C plays an important role in forming the fine grain structure in films. In those films with a high ¿eff, the lattice spacing of the (110) crystal plane of ¿-Fe is slightly (approximately 0.1%) expanded. These results suggest that the total magnetic anisotropy energy in the (110) plane of each of the ¿-Fe grains decreases owing to the induced magnetoelastic anisotropy due to tetragonal deformation.