Giant magneto-impedance effect in amorphous ferromagnetic wire with a weak helical anisotropy: Theory and experiment

An adequate description of the results of experimental measurement of both diagonal and off-diagonal Giant magneto-impedance (GMI) components has been obtained for Co-rich amorphous microwire at moderate frequencies assuming the existence of a small off-diagonal tensor component of the residual quenching stress. The latter is the origin of a weak helical anisotropy of amorphous microwire. The micromagnetic simulation of the magnetization reversal process in the microwire under the influence of the applied magnetic field and dc bias current has been carried out. It is shown that due to the influence of the magneto–elastic interaction in a wire with a weak helical anisotropy, the behavior of the longitudinal and circular magnetization components is significantly correlated. Namely, the change of the sign of the longitudinal magnetization component under the influence of the axial magnetic field leads to a subsequent jump of the circular magnetization component at some critical value of the applied magnetic field. As a result of the jump of the circular magnetization, the off-diagonal GMI component also changes sign during the wire magnetization reversal. This effect is confirmed experimentally for a Co-rich wire with a small negative magnetostriction. It is also shown that the jump of the circular magnetization can be eliminated by a circular magnetic field of a weak dc bias current flowing along the wire. This effect allows one to design sensitive magnetic field sensor based on the measurement of the off-diagonal GMI component.