N₂ partial pressure dependence of magnetic properties of FeGaN films

抄録

FeGa alloys have large saturation magnetostriction constants (λ_s) and saturation magnetization, and their good mechanical properties are expected to be applied to sensors and power generation devices. Recently, there is a need to improve soft magnetic and high-frequency properties of FeGa films for application to high-frequency devices [1,2]. Addition of light elements such as B [3] and C [4] has been reported to decrease the coercive force (H_c) and increase the λ_s. In this study, we investigated structure and magnetic properties of FeGaN films.

(Fe₈₆Ga₁₄)_1-xN_x films were prepared on a micro cover glass by dc magnetron sputtering method, using a composite target consisting of Fe₈₀Ga₂₀ chips and an Fe disk. The sputtering power and time were fixed at 27 W and 1 hour, respectively. During deposition, a dc magnetic field of about 200 Oe was applied to the substrate. The sputtering gas was a mixture of Ar and N₂ gas, and a partial pressure ratio P_N2 / P_Total, where P_N2 is the partial pressure of N₂ and P_Total is the total gas pressure, was controlled. A 30 nm thick SiN film was deposited on the surface to prevent oxidation. The magnetic properties of the films were evaluated by vibrating sample magnetometer and torque magnetometer, and the crystal structure was confirmed by X-ray diffraction (XRD).

XRD patterns revealed that the films for P_N2 / P_Total < 0.100 were crystallized, and the films for P_N2 / P_Total > 0.120 were in amorphous state.

Figure 1 shows the H_c and theλ_s as a function of P_N2 / P_Total. The H_c decreased significantly for P_N2 / P_Total > 0.100. A minimum Hc of about 1.3 Oe was obtained at P_N2 / P_Total = 0.135. The decrease in Hc is due to the structural change from crystal to amorphous. For P_N2 / P_Total > 0.135, the Hc increased due to the perpendicular magnetic anisotropy caused by non-uniform compressive stress introduced during deposition or the formation of columnar structure. The λ_s increased with increasing P_N2 / P_Total, and showed the maximum value of about 30 ppm. At P_N2 / P_Total = 0.135, the minimum Hc and the maximum λ_s were obtained, simultaneously.

References

[1] D.Cao et al. : AIP Advances 7, 115009(2017).

[2] S.Muramatsu et al : The Papers of Technical Meeting on Magnetism, IEE Jpn, MAG-21-085 (2021).

[3] J.Lou et al. : Appl. Phys. Lett. 91, 182504 (2007).

[4] S.Muramatsu et al. : The Papers of Technical Meeting on Magnetism, IEE Jpn, MAG-22-085 (2022).