Thermal stability, crystallization, and magnetic properties of FeNiBCuNb alloys

Amorphous (Fe₄₀Ni₄₀B₁₉Cu₁)_100-xNb_x (x=1, 3, 5, 7) ribbons are prepared by using the melt-spinning method. We find that the glass forming ability (GFA) of the as-melt spun ribbons is significantly improved by adding Nb element. In addition, the thermal stability evaluated in steps of ΔT=T_x2-T_x1 effectively increases from 16 K to 75 K with Nb content increasing. The as-melt spun (Fe₄₀Ni₄₀B₁₉Cu₁)₉₇Nb₃ ribbon exhibits a lowest coercivity of 2 A/m and relatively large saturation magnetization of 103.7 A·m²/kg and thus it can be further treated by being annealed at 809 K. The crystallization behavior is confirmed to be determined by two individual crystallization processes corresponding to the precipitation of (Fe,Ni)₂₃B₆ phase and γ-(Fe,Ni) phase. With increasing annealing time, the single (Fe,Ni)₂₃B₆ phase can be transformed into a mixture of (Fe,Ni)₂₃B₆ and γ-(Fe,Ni) phase, and the grain size of γ-(Fe, Ni) phase increases from 5 nm to 80 nm while the grain size of (Fe,Ni)₂₃B₆ remains almost unchanged. Finally, we find that the grain growth in each of (Fe,Ni)₂₃B₆ and γ-(Fe, Ni) deteriorates the overall magnetic properties.