Magnetization process and coercivity of Fe-(Al, Ga)-(P, C, B, Si) soft magnetic glassy alloys

The density and the magnetization process of the melt-spun glassy Fe-(Al, Ga)-(P, C, B, Si) alloys are investigated to clarify the origin of low coercivity of the glassy alloys. The differences of the density ( Δρ_c) between the crystalline and the amorphous phases of glassy Fe-(Al, Ga)-(P, C, B, Si) alloys are much smaller than those of the ordinary amorphous Fe-B(-Si) alloys. The H^-1-power law behavior of ΔJ (= J_s, - J, where J_s is the saturation magnetization) is observed for both the glassy and ordinary amorphous systems in the magnetic field (H) range of 20-25 < μ₀H ≲ 50 mT. In the high magnetic field range of 50 ≲ μ₀H < 70 mT, ΔJ of both the alloy systems obeys the H^-2-power law. The length of the effective Burgers vector and width of quasi-dislocation dipole (QDD) type defects are nearly independent of the alloy system. This means that the local volume contraction is independent of the alloy system, but the density of QDDs in the glassy alloys is much smaller than the ordinary amorphous alloys because the glassy alloys exhibit much smaller Δρ_c than the ordinary amorphous alloys. Since the coercivity originates from elastic stress of QDDs is proportional to (Δρ_c)^1/2, the origin of low coercivity of the Fe-(Al, Ga)-(P, C, B, Si) glassy alloys is the low density of QDDs which corresponds to low density of the domain-wall pinning centers.