Effect of annealing on magnetoimpedance of Co68Fe4Zr10Cu2B16 ribbons

Magnetoimpedance (MI) in Co68Fe4Zr10Cu2B16 alloy has been investigated in the frequency range 500 kHz-5 MHz and with the application of external steady magnetic field in the longitudinal direction, up to 100 Oe. MI measurements were carried out on as-cast ribbons and also on conventionally annealed and Joule-annealed ribbons. In as cast ribbons, the maximum MI observed is 13% at a frequency of 500 kHz and it decreases to 5% and 4% with conventional annealing at 100'C and 150'C, respectively. On the other hand, MI decreases to 8 % and 6% with Joule annealing employing currents of 100 mA and 200 mA, respectively. However, Joule annealing with the application of a magnetic field of 5-10 Oe in the transverse direction causes the MI to decrease to 12% and 11 % for currents of 100 mA and 200 mA, respectively. In the as-cast ribbons, double peak behavior is observed in all the frequencies whereas, in the annealed ribbons, double peak behavior in general is observed only at high frequencies.