Magnetic characteristics of Fe-N films prepared by reactive ion beam sputtering with a nitrogen bombardment process

Fe-N films were prepared by reactive ion beam sputtering with a nitrogen bo mbardment at the ratio in arrival rate of nitrogen ions to sputtered iron a toms of 0.1, of which the value was nearly equal to the Fe16N2 composition. The voltage for nitrogen bombardment V-A was varied in the range between 8 0 and 2000 V. The nitrogen content of the Fe-N films was in the range of 8- 13 at. %. The phase of the films changed from alpha' to alpha+gamma' at V-A higher than 400 V. The saturation magnetization 4 pi M-S of the films took the large value in the range of 22-23.5 kG at V-A lower than 200 V. 4 pi M -S with the alpha+gamma' phase was smaller than pure Fe ones. The films exh ibited a large perpendicular magnetic anisotropy field to 3.4 kOe with an i ncrease of V-A. After the films of alpha' phase prepared at V-A of 100 V we re postannealed, the films appeared at the gamma' phase from the annealing temperature T-A of 400 degrees C. 4 pi M-S of the films decreased gradually with an increase of T-A in the range higher than 300 degrees C and was sma ller than that of pure Fe at T-A of 400 degrees C. These results indicate t hat the energy of the nitrogen bombardment should impact significantly the phase of the films by the thermal effects of the bombardment energy and the energy below 200 eV may be suitable for preparing the Fe-N films with larg e 4 pi M-S. (C) 2000 American Institute of Physics. [S0021-8979(00)27808-0] .