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.
The asymmetric giant magnetoimpedance (GMI) profile has been realized in weak-field-annealed Co-based amorphous ribbon at the annealing temperature of 380 °C in open air. Asymmetric GMI profiles with respect to applied field become profound as the annealing field increases over 500 mOe. The asymmetric GMI profile at the frequencies of ac current over 0.5 MHz is well ascribed for by the rotational transverse magnetization of single domain under a uniaxial anisotropy in amorphous core and a unidirectional anisotropy due to the exchange coupling with the bias field in the crystalline layer, underlying surface oxidation layer developed during the annealing in open air.
In a Comment [D. X. Chen, L. Pascual, and A. Hernando, Appl. Phys. Lett. 77, 1727 (2000)] on our recent letter [C. G. Kim, K. J. Jang, D. Y. Kim, and S. S. Yoon, Appl. Phys. Lett. 75, 2114 (1999); 76, 1345 (2000)] Chen et al. claimed that the unidirectional anisotropy due to bias field is unphysical one for the description of asymmetric giant magnetoimpedance (GMI) profiles. The symmetric two peaks of GMI profiles measured in the normal sample with an uniaxial anisotropy, allow one to take the minimum energy condition which assumes a jump of magnetization under the field from a metastable state to a stable one. However, the divergence in a calculated GMI profile should appear even in case of a uniaxial anisotropy of normal sample where there is no jump. Divergence indicates the asymmetry and hysteresis in GMI profile. The analysis of this calculation in Chen et al.’s Comment is simply a matter of hysteresis in GMI profile for the increasing and decreasing field, even in a normal sample with uniaxial anisotropy. Even though the hysteresis is ignored by taking the minimum energy condition, the asymmetric profiles with the negligible hysteresis are well ascribed by the model with two kinds of anisotropy fields, as proposed in our previous letter [C. G. Kim, K. J. Jang, D. Y. Kim, and S. S. Yoon, Appl. Phys. Lett. 75, 2114 (1999); 76, 1345 (2000)]. In this model the bias field is quite physical, and is based on the observed experimental results in a specially prepared sample.
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