A model for asymmetric giant magnetoimpedance in field-annealed amorphous ribbons

Abstract

A phenomenological model for the asymmetric giant magnetoimpedance (GMI) in fieldannealed amorphous ribbons is developed. The effect of a surface crystalline layer on the GMI response is described in terms of an effective bias field appearing due to a coupling between the crystalline layer and amorphous phase. It is shown that the presence of the bias field changes drastically the GMI profile. At low frequencies, the domain-walls motion leads to a steplike change in the GMI response. At high frequencies, the domain-walls motion is damped, and the GMI profile exhibits asymmetric two-peak behavior. The calculated dependences are shown to be in a qualitative agreement with results of experimental studies of the asymmetric GMI in field-annealed Co-based amorphous ribbons.

Off-diagonal magnetoimpedance in field-annealed Co-based amorphous ribbons

“…9 The transition from the single-peak to two-peak field dependence of the impedance can be explained as follows. 23 At low frequencies, the main contribution to the permeability is due to the domain-walls motion, and in this case the GMI response has the single-peak behavior. At high frequencies, the domain-walls motion is damped by eddy currents, and the magnetization rotational process determines the permeability, which results in the two-peak GMI profile.…”

“…The details of the averaging procedure can be found in Ref. 23. It should be noted that the presence of the domain structure reduces the off-diagonal impedance due to the contribution with opposite sings from the domains with different transverse magnetization direction.…”

“…Moreover, the bias field changes the relative volume of two types of domains. 23 These two factors result in nonzero off-diagonal magnetoimpedance even in the presence of domain structure, since the signals from the domains are not compensated completely. Note also that we assume in calculations that the saturation magnetization, conductivity, and damping parameter are the same for the amorphous and crystalline regions.…”

“…This fact can be understood in the following way. The contribution from the domain-walls motion to the transverse permeability, µ tr , which is responsible for the GMI measured as the voltage across the sample, is given by 23 …”

A model for exchange-biased asymmetric giant magneto-impedance in amorphous wires

“…Because the crystalline phase is the hard magnetic one, it remains magnetically ordered within a relatively wide range of magnetic fields. The exchange coupling between the crystalline and amorphous phases produces an effective bias field resulting in asymmetry in the dc magnetization of the amorphous bulk that is responsible for the asymmetric GMI in field-annealed ribbons [3,5,7,8].…”