Optimization of giant magnetoimpedance in Co-rich amorphous microwires

The dependences of the magnetoimpedance ratio ΔZ/Z of soft magnetic Co₆₇Fe_3.85Ni_1.45B_11.5Si_14.5Mo_1.7 glass-coated amorphous microwires with various geometric ratio ρ upon axial magnetic field H has been measured for the frequency f range 0.06-15 MHz, driving current amplitude I of 0.75-2 mA, and H up to 2400 A/m. Surface hysteresis loops have been measured by transverse magnetooptical Kerr effect (MOKE). A maximum relative change in the giant magnetoimpedance (GMI) ratio ΔZ/Z up to around 615% is observed at f=10 MHz and I=0.75 mA in the sample with ρ≈0.98. Application of dc bias current strongly affects the GMI ratio. A maximum of GMI ratio occurs approximately at the same field as the coercivity of surface loops.