SOFT-MAGNETIC PROPERTIES OF CO-BASED AMORPHOUS-ALLOYS WITH WIDE SUPERCOOLED LIQUID REGION

New Co-based amorphous alloys with a wide supercooled liquid region ab ove 40 K before crystallization and good soft magnetic properties were synthesized in the Co72-xFexZr8B20 and Co63Fe7Zr10-xMxB20 (M=Nb, Ta o r W) systems. The supercooled liquid region defined by the difference between crystallization temperature (T-x) and glass transition tempera ture (T-g), Delta T-x(= T-x - T-g), is 39 K for Co56Fe16Zr8B20, 45 K f or Co63Fe7Zr6Nb4B20, 40 K for Co63Fe7Zr4Ta6B20 and 44 K for Co63Fe7Zr6 W4B20. The glass transition is also observed for the Co63F7M10B20 (M = Ta or W) alloys. The Co-based amorphous alloys with Delta T-x above 4 0 K 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 (mu(e)) of 10000 to 23000 at 1 kHz. The good mu(e) characteristics are maintained in a hi gh frequency range and the mu(e) at 1 MHz is 5700 for Co56Fe16Zr8B20 a nd 6800 for Co63F7Zr6Ta4B20. The high frequency permeability is superi or to those for conventional Co- and Fe-based amorphous alloys. The el ectrical resistivity (rho(n)) is as high as 1.7 to 2.0 mu Ohm m and he nce the reduction of eddy current loss caused by the high rho(n) is pr esumed to be the origin of the better high-frequency permeability. The simultaneous achievements of good soft magnetic properties and high r ho(n) are presumably due to the formation of a unique amorphous struct ure 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 sub nanoscale, because the former type pair has good soft magnetic propert ies and the latter type pair has high rho(n). The good combination of high stability of the supercooled liquid and good soft magnetic proper ties is expected to induce future development as a new type of soft ma gnetic bulk amorphous alloy.