Soft Magnetic Properties of Fe-N Films Composed of Two Phases.

Fe-N films were synthesized by means of ion beam deposition techniques. Nitrization was performed by using an assist gun during the sputtering of Fe films. As deposited Fe-N films composed of two phases, α-Fe and γ′-Fe4N, had a large coercive force (Hc) of over 20 Oe. When the films were annealed in a vacuum, their Hc improved drastically, and had a minimum value of less than 1 Oe at 400°C. The films also had a high permeability of over 2000 as well as high resistivity (around 80 μΩcm) in spite of a high saturation magnetization (around 18 kG). The small grain size and stress relaxation in the films were closely related to the soft magnetic properties. The volume fraction of the γ′-Fe4N phase also affected the decrease in Hc, because the anisotropy normal to the film plane was reduced by increasing the magnetostatic energy when the volume fraction was 0.5.