Optimizing the magnetic and giant magneto-impedance (GMI) properties of glass-coated amorphous Co-based wires via single- and two-step direct current annealing

The effects of both single- and two-step direct current (DC) annealing procedures on the magnetic properties (including the giant magneto-impedance (GMI)) of glass-coated Co66Fe6Si13B15 amorphous wires were evaluated. For both methods, the GMI ratio initially increased with the current intensity and reached a peak value before declining at higher current intensities. A maximum improvement of the GMI ratio of about five times was obtained for the two-step DC-annealed sample, while that for single-step DC-annealed samples was only 2.44 times. A higher GMI sensitivity was also observed for the two-step DC-annealed wires. The better GMI performance of the two-step DC annealed samples was attributed to the more homogeneously distributed precipitation in the matrix and the ordered circumferential magnetic domains on the surface. The results obtained further imply that DC annealing at a higher current intensity but over a shorter treatment time is a more efficient and energy-saving method for enhancing the GMI performance of Co-based amorphous wires for potential industrial applications.