High-frequency permeability characteristics of Fe- and Co-based amorphous alloys with high B concentrations

New Fe-based and Co-based amorphous alloys with a high B concentration of 30 at% were formed in the (Fe,Co,Ni)₆₂Nb₈B₃₀ system. The amorphous alloys exhibit a wide supercooled liquid region (ΔT_x) above 80 K before crystallization in the range of 5 to 40% Co and 0 to 10% Ni and the largest ΔT_x is 87 K for Fe₅₂Co₁₀Nb₈B₃₀. The Fe _62-xCo_xNb₈B₃₀ alloys exhibit good soft magnetic properties i.e., low coercive force (H_c) of 2-3 A/m, high effective permeability (μ_e) of 20000-30000 at 1 kHz and low saturated magnetostriction (λ_s ) of 2-8×10 d. The high μ_e characteristics are maintained in a higher frequency range and the highest μ_e at 1 kHz is 7500 for Co₄₀Fe₂₂Nb₈B₃₀ with a high resistivity of 237 μΩ cm. The finding of the (Fe,Co)₆₂ Nb₈B₃₀ amorphous alloys exhibiting large ΔT_x, good high-frequency permeability and high resistivity is encouraging the future development as a new soft magnetic materials