Structure and Soft Magnetic Properties of Fe-N Thin Films RF-Sputtered on Heated Substrate

The film structure and the soft magnetic properties of Fe-N films prepared by the RF reactive sputtering method at a substrate temperature of 473 K were investigated. It was shown that the substrate heating during film deposition is effective in improving the soft magnetic property of the Fe-N film. As the ratio R(=PN2⁄Ptotal) of the N2 gas pressure to the (Ar+N2) gas pressure in the sputtering gas increased, the film structure of the α-Fe single phase changed to a mixture of α-Fe and γ′-Fe4N. The lowest coercive force (Hc=63.6 A/m) and the highest initial permeability (μ′=1500 at 1 MHz) of the film were obtained under a sputtering condition of R=8%. Under this condition, the film maintained a high magnetic flux density (Bs=21.6 T) which value is the same as that of bulk Fe. The excellent soft magnetic property was obtained when the film was a mixture of fine grains of α-Fe and γ′-Fe4N without any preferential orientation. At R=3∼5%, Bs value of the film exceeded the one of pure Fe, and the maximum value of Bs=2.44 T was obtained. This was attributed to the nitrogen solution to the α-Fe matrix.