Magnetic properties of Fe-N/Fe multilayered films deposited by an opposed targets sputtering

Fe-N/Fe multilayer films have been deposited by an opposed-target sputtering apparatus and their magnetic properties were investigated. Coercive force, H_c, of the Fe-N/Fe multilayer film takes a minimum value at a proper nitrogen content and decreases as the length of the layer period d_layer increases. This decrease in H_c is mainly due to the decrease in perpendicular magnetic anisotropy of the film. The film with a d_layer of 1480 Å has an H_c of 1.5 Oe and a saturation magnetization of 1600 emu/cm³. Annealing at a temperature above 200°C leads to the crystallization of the α-Fe and γ´-Fe₄N in the film. Diffusion of the nitrogen atoms from the Fe-N layer to the Fe layer becomes significant at a temperature above 400°C, and the layered structure in the film is removed by annealing at a temperature above 450°C. The H_c of the film takes a value in the range from 1 to 5 Oe irrespective of d_layer and nitrogen gas flow rate if the film is annealed at a temperature above 350°C