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)/sub 62/Nb/sub 8/B/sub 30/ system. The amorphous alloys exhibit a wide supercooled liquid region (/spl Delta/T/sub x/) above 80 K before crystallization in the range of 5 to 40% Co and 0 to 10% Ni and the largest /spl Delta/T/sub x/ is 87 K for Fe/sub 52/Co/sub 10/Nb/sub 8/B/sub 30/. The Fe/sub 62-x/Co/sub x/Nb/sub 8/B/sub 30/ alloys exhibit good soft magnetic properties i.e., low coercive force (H/sub c/) of 2-3 A/m, high effective permeability (/spl mu//sub e/) of 20000-30000 at 1 kHz and low saturated magnetostriction (/spl lambda//sub s/) of 2-8/spl times/10 d. The high /spl mu//sub e/ characteristics are maintained in a higher frequency range and the highest /spl mu//sub e/ at 1 kHz is 7500 for Co/sub 40/Fe/sub 22/Nb/sub 8/B/sub 30/ with a high resistivity of 237 /spl mu//spl Omega/ cm. The finding of the (Fe,Co)/sub 62/Nb/sub 8/B/sub 30/ amorphous alloys exhibiting large /spl Delta/T/sub x/, good high-frequency permeability and high resistivity is encouraging the future development as a new soft magnetic materials.