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

Abstract

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 (Tx) is 899 K for the Co–Zr–B alloys and remains unchanged in the Fe concentration range up to 20%. The glass transition temperature (Tg) decreases with increasing Fe content, and the ΔTx(=Tx−Tg) 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 Co-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 1–103 kHz and low magnetostriction between −1.5×10−6 and +10×10−6 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.