Enhanced initial permeability and magneto-impedance ratio of Co67Fe4Mo2Si15B12

Co-based amorphous alloy exhibits superior soft magnetic properties after appropriate annealing treatment below the crystallization temperature by devitrification of the amorphous phase. The initiation of crystallization temperature has been found as 518 °C from differential thermal analysis for the heating rate of 10 °C/min. Ultra-soft magnetic properties manifested by enhanced initial permeability, μ′ of the order of 5.1 × 104 and reduction of relative loss factor, tan δ/μ′ of the order of 9 × 10− 6 has been achieved for the annealing temperature of 500 °C for 30 min. This has been achieved because at this stage local anisotropy is averaged out by exchange coupling between nanograins embedded in the residual amorphous matrix. Since enhanced magneto-impedance is a typical characteristic of Co-based amorphous alloy, field dependence of magneto-impedance has been measured for as-cast and annealed samples at current driving frequency of 4.5 MHz. Field dependence of magneto-impedance shows hysteresis at low field, which is related to the changes in the magnetization process of the sample.