Study of magnetoimpedance effect in Co–Fe–Si–B glass-covered microwires

Thermal annealing, ac drive current and frequency dependence of magnetoimpedance (MI) effect in amorphous Co68.25Fe4.5Si12.25B15 glass-covered microwires is reported. Thermal annealing affects the circular permeability of the circumferentional domain structure thus modifying (influencing) the maximum magnetoimpedance ratio (ΔZ/Z)max and its sensitivity to applied magnetic field S. Reduction of S after annealing is attributed to the reduced value of (ΔZ/Z)max. Maximum magnetoimpedance ratio up to 71% and the sensitivity to magnetic field S of 24.5%/Oe at 3 MHz and 4 mA is obtained for as-prepared microwire. S and (ΔZ/Z)max shows a stronger dependence on frequency as compared with ac drive current amplitude. Most attractive feature of the present work is reasonably high (ΔZ/Z)max and S at relatively low frequencies, useful for potential application in magnetic field sensors.