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

The film structures and soft magnetic properties have been investigated for Fe–N films prepared by RF reactive sputtering at a substrate temperature of 473 K. The substrate heating during film deposition is effective in improving the soft magnetic property of the Fe–N film. As the ratio of the N2 gas pressure to the (Ar+N2) gas pressure, R=(PN2⁄Ptotal) in the sputtering gas increases, the film structure changes from the α-Fe single phase 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) are obtained for the film prepared under a sputtering condition of R=8%. This film maintains a high magnetic flux density (Bs=2.16 T) which is the same as that of bulk Fe. The excellent soft magnetic property is obtained when the film is a mixture of fine grains of α-Fe and γ′-Fe4N without any preferential orientation. At R=3∼5%, the Bs value of the film exceeds that of pure Fe, and the maximum value is Bs=2.44 T. This is attributed to the nitrogen incorporation in the α-Fe matrix.