Semi-hard magnetism of iron nitride films prepared by double ion beam sputtering

The semihard magnetic properties and crystal structure of iron nitride films prepared by double ion beam sputtering have been investigated. The films consisted of Fe layers and Fe_xN layers bombarded by nitrogen ions during deposition. The films were annealed at 300°C for 3 h after deposition. When the thickness ratio of Fe layers to Fe_xN was adjusted to a value below 10 for films with the appropriate number of pairs of layers, the as-deposited films had coercivity, H_c of about 100 Oe and saturation magnetization, 4πM_s, of about 18 kG. Annealing of films composed of 19 pairs of Fe and Fe_xN layers with a relative thickness ratio of 5 resulted in a large increase in film coercivity from less than 100 Oe before anneal to 500 Oe postanneal. A moderate decrease in film 4πM_s was also seen after the annealing process. X-ray diffractometry showed the presence of ζ-Fe₂N phase in these films. A moderate decrease of 4πM_s and a marked increase of H _c may be caused by suppressing the growth of ζ-Fe ₂N crystallites and the short-range irregularity at interfaces between Fe and Fe_xN layers