Influence of Ar Pressure on the Magnetic Properties of Amorphous FeGaSiB Thin Films

Abstract

Magnetostrictive amorphous FeSiB and FeGaSiB thin films, thickness 50nm have been grown by the co-sputtering-evaporation technique with a range of Ar pressure (4 -8 bar) to control the Ga percentage within the films and study their effect on the magnetic, structural and magnetostriction properties. By x-ray diffraction, it was found that all the films had an amorphous structure and the only peaks present were for Si substrate. Using a magneto-optical Kerr effect (MOKE) magnetometer, it found that, for the FeSiB films, the anisotropy field (Hk) increased slowly as the pressure increased, while for the FeGaSiB films, the saturation field (Hs) ≈ 4000 A/m for all pressures. For both the film sets, the coercive field (Hc) was less than 800 A/m. The magnetostriction constants (s) of the FeSiB thin films increased with increasing pressure. While for the FeGaSiB films, the magnetostriction constant decreased with increasing the sputtering gas pressure, with the maximum = 11.4 ppm, at the lowest pressure 4 bar. Thus it was determined that the addition of Ga atoms reduced the intrinsic stress within the films, while maintaining the amorphous morphology.

Influence of Ga evaporation rate on the magnetic properties of Amorphous FeGaSiB thin films

“…For thicknesses ≥40 nm, the FeGaSiB magnetostriction constants were all larger than the FeSiB films magnetostriction constants. While changing the sputtering gas pressure at fixed Ga rate (0.2 a.u), for 50nm FeGaSiB film [19] did not affect the morphology of the films, but the magnetostriction constant decreased with increasing Ar pressure. This work extends our previous study, by using the optimised fabrication parameters (sputtering power (20W) and pressure (4 µbar)) determined from our previous papers [18,19] and increasing the Ga concentration by increasing the Ga rate to investigate how a larger amount of Ga in the ratio FeSiB:Ga in these films, effects the morphology, magnetic properties, and magnetostriction constant (s) of FeGaSiB thin films.…”

“…Thus for the film at Ga 7%, D ≈ 0.3, so has weak uniaxial anisotropy, while a stronger uniaxial anisotropy is present in the film at Ga 8% where D ≈ 0.83 (see Figure 4). FeSiB film grown with the same fabrication parameters and Hk ≈ 2300 A/m [18,19], the FeGaSiB films all have a higher anisotropy field. The anisotropy energy depends on the anisotropy constant, which is given by eqn (2).…”

“…Thus, the 14% Ga film, has less pinning compared to the 7% Ga film, so a smaller Mr/Ms along the hard axis, this leads to the observation of strong uniaxial anisotropy observed in Figure 3 inset, but as it has a smaller Ms compared to the 7% Ga film but the same Hk, so the anisotropy constant, hence energy is smaller compared to the 7% Ga film. [18,19] of Hc ≈ 800 A/m. This means that the Ga addition has reduced the coercive field, probably due to reduced domain wall pinning in the higher concentration films, as suggested by the Mr/Ms data.…”

“…Our previous work [18] on FeSiB and FeGaSiB thin films grown on Si substrate using a cosputtering-evaporation technique determined how film thickness and sputtering pressure [19] affected the structural and magnetic properties. These results showed that adding Ga to amorphous FeSiB films in the thickness range 24-100 nm did not affect the morphology of the films, but the magnetic properties and magnetostriction constants were changed.…”