Influence of current annealing on the magneto-impedance response of co-based ribbons arising from surface structural improvement

In this paper, influence of current annealing on the magneto-impedance (MI) response of the Co-based amorphous ribbons with chemical composition of Co68.15Fe4.35Si12.5B15 was investigated. In order to achieve a maximum MI ratio, ribbon samples were annealed under two different conditions: the atmospheric pressure and a vacuum pressure of 5 x 10(-3) mbar. During the annealing process, the dc electric current passing through the ribbons improved the surface structure while also changing the magnetic properties, arising from heating of the samples under proper conditions. The annealing process not only induced transverse magnetic anisotropy in the ribbon but also decreased stresses generated during melt spinning processes, thus enhancing the corresponding MI response. Annealing at different times and currents were performed in order to achieve optimum conditions and reach the maximum MI. Our results showed that the MI ratio increased for the annealed samples at both vacuum and atmospheric pressures so that the maximum MI (288%) was obtained for current annealing (at 200 mA for 65 s) in the vacuum, being promising for sensor applications. On the other hand, AFM and XRD results confirmed that less surface roughness would provide a smaller stray field, which in turn would increase the MI ratio.