Soft Magnetic Properties of Co-Based Amorphous Alloys with Wide Supercooled Liquid Region

Abstract

New Co-based amorphous alloys with a wide supercooled liquid region above 40 K before crystallization and good soft magnetic properties were synthesized in the Co 72-x Fe x Zr 8 B 20 and Co 63 Fe 7 Zr 10-x M x B 20 (M=Nb, Ta or W) systems. The supercooled liquid region defined by the difference between crystallization temperature (T x ) and glass transition temperature (T g ), ΔT x (=T x -T g ), is 39 K for Co 56 Fe 16 Zr 8 B 20 , 45 K for Co 63 Fe 7 Zr 6 Nb 4 B 20 , 40 K for Co 63 Fe 7 Zr 4 Ta 6 B 20 and 44 K for Co 63 Fe 7 Zr 6 W 4 B 20 . The glass transition is also observed for the Co 63 Fe 7 M 10 B 20 (M=Ta or W) alloys. The Co-based amorphous alloys with ΔT x above 40K exhibit low coercivity of 2.5 to 5.6 A/m, low magnetostriction of 1.7 x 10 -6 to 3.0 x 10 -6 and high permeability (μ e ) of 10000 to 23000 at 1 kHz. The good μ e characteristics are maintained in a high frequency range and the μ e at 1 MHz is 5700 for Co 56 Fe 16 Zr 8 B 20 and 6800 for Co 63 Fe 7 Zr 6 Ta 4 B 20 . The high frequency permeability is superior to those for conventional Co- and Fe-based amorphous alloys. The electrical resistivity (ρ n ) is as high as 1.7 to 2.0 μΩm and hence the reduction of eddy current loss caused by the high ρ n is presumed to be the origin of the better high-frequency permeability. The simultaneous achievements of good soft magnetic properties and high ρ n are presumably due to the formation of a unique amorphous structure in which two kinds of atomic pairs of metal-metal (Co-Fe-Zr-M) and metal-metalloid (Co-Fe-Zr-M-B) types are homogeneously mixed on a subnanoscale, because the former type pair has good soft magnetic properties and the latter type pair has high ρ n The good combination of high stability of the supercooled liquid and good soft magnetic properties is expected to induce future development as a new type of soft magnetic bulk amorphous alloy.