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 Co_70-xFe_xZr₁₀B₂₀ and Co_72-xFe_xZr₈B₂₀ 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 ΔT_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 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 5500-18300 in the frequency range of 1-10³kHz 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.