Current Annealings and Magnetoimpedance in Co-Fe Amorphous Ribbons

Amorphous ribbons of composition (Co$\text{}_{0.95}$Fe$\text{}_{0.05}$)$\text{}_{100-x}$Si$\text{}_{0.4x}$ B$\text{}_{0.6x}$, with x=25 and 30 were prepared by the melt-spinning technique. Current annealings at 600 mA were performed for annealing times between 15 s and 60 min. The magnetoimpedance response was investigated by submitting the ribbons to ac currents at frequencies in the 10-200 kHz range, with amplitudes between 1 and 15 mA (rms), and measuring their voltage response. The observed results show that a transverse anisotropy is induced by the thermal treatments, which can be evaluated by means of the magnetoimpedance effect. Due to its lower Curie temperature, the x=30 ribbons exhibited lower sensibility to the current annealings.