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 ${\mathrm{Co}}_{\text{70−x}}{\mathrm{Fe}}_x{\mathrm{Zr}}_{\mathrm{10}}{\mathrm{B}}_{\mathrm{20}}$ and ${\mathrm{Co}}_{\text{72−x}}{\mathrm{Fe}}_x{\mathrm{Zr}}_{\mathrm{8}}{\mathrm{B}}_{\mathrm{20}}$ alloys containing more than 14 at % Fe. The crystallization temperature ${\mathrm{(T}}_x)$ is 899 K for the Co–Zr–B alloys and remains unchanged in the Fe concentration range up to 20%. The glass transition temperature ${\mathrm{(T}}_g)$ decreases with increasing Fe content, and the ${\mathrm{\Delta T}}_x{\mathrm{(=T}}_x{\mathrm{-T}}_g)$ 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 ${\mathrm{Co}}_{\mathrm{3}}{\mathrm{ZrB}}_{\mathrm{2}}$ 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 ${\text{1–10}}^3\hspace{0.17em}\mathrm{kHz}$ and low magnetostriction between ${\text{−1.5×10}}^{\text{−6}}$ and ${\text{+10×10}}^{\text{−6}}$ 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.