Excellent soft magnetic Fe-Co-B-based amorphous alloys with extremely high saturation magnetization above 1.85 T and low coercivity below 3 A/m

Abstract Extremely good soft magnetic properties of high saturation magnetization ( B s ) above 1.8 T and low coercivity ( H c ) below 5 A/m were obtained for (Fe 1- x Co x ) 83 B 16 Si 1 ( x = 0.1–0.3) amorphous ribbons annealed at the temperature between T x1 -120 K and T x1 -40 K. Here T x1 is the onset temperature of the first exothermic crystallization peak. The best characteristics were 1.86 T for B s and 3 A/m for H c at x = 0.2. There are no previous data on the melt-spun alloys with high B s above 1.8 T and low H c below 5 A/m and hence the present amorphous alloys are regarded as a novel good soft magnetic alloy with high B s comparable to Fe-Si steels. Curie temperature ( T c ) of the x = 0.2 alloy was above T x1 (708 K), implying high thermal stability of magnetic characteristics. The saturated magnetostriction for x = 0.2 was about 32 ppm and the effective permeability at 1 kHz showed as high as 1.6 × 10 4 . The high B s can be attributed to the low metalloid content containing mainly B element which suppresses effectively the reductions of B s and T c among metalloid elements, as well as the optimum Co/Fe content ratio with the maximum magnetic interaction in conjunction with maximum atomic volume. Moreover, these alloy ribbons exhibited good bending ductility even after optimum annealing treatment, in addition to high Vickers hardness of about 1000 and improved corrosion resistance comparing with the corresponding Co-free alloy. The excellent soft magnetic amorphous alloys are promising for further extension as engineering soft magnetic materials.