Ferromagnetic Co-Fe-Zr-B amorphous alloys with glass transition and good high-frequency permeability

A Co-based amorphous phase with glass transition and supercooled liquid region before crystallization was formed in Co70-xFexZr10B20 and Co72-xFexZr8B20 alloys containing more than 14 at % Fe. The crystallization temperature (T-x) is 899 K for the Co-Zr-B alloys and remains unchanged in the Fe concentration range up to 20%. The glass transition temperature (T-g) decreases with increasing Fe content, and the Delta T-x(= T-x-T-g) increases from 25 K at 14% Fe to 34 K at 21% Fe. The amorphous alloys with glass transition crystallize with a single stage precipitation of bcc Fe(Co) and Co3ZrB2 phases. The Go-rich amorphous alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.58-0.83 T, low coercivity of 4.7-8.3 A/m, and high permeability of 5500-18 300 in the frequency range of 1-10(3) kHz and low magnetostriction between - 1.5 x 10(-6) and + 10 x 10(-6) including zero. The success in synthesizing the soft magnetic amorphous alloys with high stability of supercooled liquid is promising for the future development of ferromagnetic Co-based bulk amorphous alloys. (C) 1998 American Institute of Physics.