Ultra-soft magnetic properties and giant magneto-impedance of Co68Fe4.5Si12·5B15

We have prepared an amorphous Co68Fe4.5Sil2·5B15 alloy, annealed it in the temperature range of 200–580 °C and carried out a detailed study of the effect of crystallization on its magnetic properties. When annealed in an optimized condition, a very high value of initial permeability of the order of ~ 104 has been attained in association with a drastic decrease of the relative loss factor. This change of properties has been attributed due to the formation of nanograins of fcc Co and Co3B, as identified by X-ray diffraction and differential thermal analysis. The activation energy of crystallization is 4.18 eV. Hysteresis loop parameters were then extensively studied for the samples annealed at various temperatures. Finally, a very high value of giant magneto-impedance (GMI)—which is a characteristic property of Co-based amorphous alloys derived from well defined anisotropy axis (around 375) has been observed for a sample annealed at 380 °C.