Effect of Co content on structure and magnetic behaviors of high induction Fe-based amorphous alloys

Abstract

The replacement of Fe with Co is investigated in the (Fe1−xCox)79Si8.5B8.5Nb3Cu1 (x=0, 0.05, 0.2, 0.35, 0.5) amorphous alloys. The alloys are synthesized in the forms of ribbons by single roller melt spinning technique, and the structural and magnetic properties of annealed ribbons are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM), B–H curve tracer, respectively. All as-cast alloys are structurally amorphous, however, their magnetic properties are varying with Co addition. The Co addition within 5–20at% results in moderate thermal stability, saturation induction, Curie temperature and lowest coercivity, while 35at% Co causes highest saturation induction, coercivity, Curie temperature and lowest thermal stability. On devitrification, the magnetic properties change with the generation of α-FeCo nanocrystallites and (FeCo)23B6, Fe2B phases during primary and secondary crystallization stages, respectively. A small amount Co is advantageous for maintaining finer nanocrystallites in amorphous matrix even after annealing at 600°C, leading to high saturation magnetization (>1.5T) and low coercivity (~35A/m). The improved magnetic properties at elevated temperatures indicate these alloys have a potential for high frequency transformer core applications.