Giant magnetoimpedance in glass-covered amorphous microwires at microwave frequencies

In this work, results on the giant magnetoimpedance (GMI) of a glass-covered amorphous microwires with nominal compositions Co_70.4Fe_4.6Si₁₅B₁₀ and Fe_77.5Si_7.5B₁₅ are presented. The impedance Z=R+iX has been investigated as function of frequency (up to 1.8 GHz) and magnetic field (up to ±400 Oe), using a HP4396B impedance analyzer and an appropriate coaxial microwave cavity. The effects of the thermal treatments (Joule heating, from 20 mA up to 100 mA for 10 min) for anisotropy induction and, as a consequence, for GMI effect have been investigated.