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

Fe-N films were synthesized by means of ion beam deposition. Nitridation was performed using an assist gun during the sputtering of Fe films. The as-deposited Fe-N films consisted of two phases, μ-Fe and γ'-Fe
₄
N, and had a high coercive force H
_c
of over 20 Oe. When the films were annealed in vacuum, their H
_c
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 μΩ-cm), in spite of a high saturation magnetization (around 18 kG). The small grain size and stress relaxation in the films are closely related to the soft magnetic properties. The volume fraction of the γ'-Fe
₄
N phase also affected the decrease in H
_c
, because the anisotropy normal to the film plane is reduced by increasing the magnetostatic energy when the volume fraction was 0.5.