Asymmetric giant magnetoimpedance in field-annealed Co-based amorphous ribbon

Abstract

The giant magnetoimpedance (GMI) has been measured in weak-field-annealed Co-based amorphous ribbon as functions of both the annealing field, Ha, and the measuring frequency. The GMI profile measured at 0.1 MHz shows a typical two-peak behavior for the sample with Ha less than 50 mOe. The GMI peak in the region where the applied field is antiparallel to the annealing field decreases with Ha, showing an asymmetry in the GMI profile. Eventually, the GMI peak in the antiparallel-field region disappears, and a drastic step-like change in the GMI peak is revealed for an applied field which is parallel to the annealing field of 500 mOe. The asymmetric GMI phenomenon for the 0.1 MHz measuring frequency, the so-called “GMI valve,” is due to a peculiar domain structure, which occurs in the sample surface during the field annealing. The GMI peak in the parallel-field region appears again for measuring frequencies over 0.5 MHz due to the remarkable contribution of the magnetization rotation to the GMI.

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

“…11 The coupling between the crystalline and amorphous phases produces an effective bias field resulting in the asymmetry in the dc magnetization that is responsible for the asymmetric GMI in field-annealed ribbons. 6,9 At sufficiently low frequencies, the GMI profile exhibits a drastic steplike change in the impedance near zero field (the so-called "GMI valve"), and at high frequencies, the field dependence of the impedance shows asymmetric two-peak behavior. 9 It should be noted that the peaks at the GMI field dependence are reversed if the applied field exceeds some value of the order of several hundreds of Oe.…”

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

“…This type of the asymmetric GMI has been observed in Co-based amorphous ribbons annealed in air in the presence of a weak magnetic field applied along the sample axis [3,4]. Since the ribbons annealed in vacuum did not show the asymmetry [3,5], the phenomenon has been attributed to oxidation and surface crystallization.…”

“…This type of the asymmetric GMI has been observed in Co-based amorphous ribbons annealed in air in the presence of a weak magnetic field applied along the sample axis [3,4]. Since the ribbons annealed in vacuum did not show the asymmetry [3,5], the phenomenon has been attributed to oxidation and surface crystallization. The field-annealing in air produces asymmetric hysteresis loops in amorphous ribbons due to the exchange interaction of the amorphous bulk with the magnetically harder crystalline surface layers [6].…”

“…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].…”

Asymmetric Magnetoimpedance in Bimagnetic Multilayered Film Structures

“…This type of the AMI has been observed initially in field-annealed amorphous ribbons [6,7]. For film structures, the AMI has been studied extensively in the exchange bias multilayers [8,9].…”