Hysteresis in Asymmetrical GMI Effect in Amorphous Microwires

The double-peak behaviour of giant magneto-impedance (GMI) dependence on the external magnetic field strength H is observed in as-cast glass-covered amorphous thin wire $Co_{70.5}Fe_{4.5}Si_{15}B_{10}$ (microwire), as well as in microwire with the removed glass cover. The position of sharp peaks is symmetrical (H=± $H_{m}$) with respect to zero external magnetic field strength (H=0) and corresponds to the critical field of irreversible magnetization rotation. The maximum GMI ratio $(ΔZ//Z)_\text{max}$ dependence on the amplitude of current $i_{ac}$ at frequency of 1 MHz is analysed by means of the helical anisotropy (0<α<90°), induced during preparation of the microwire and after glass-cover removing. The additional dc bias current $i_{dc}$ ≤ $i_{ac}$ is applied in order to achieve asymmetrical GMI effect. Asymmetrical GMI dependences exhibit hysteresis which can be explained by irreversible magnetization rotation at ferromagnetic surface of the microwire.