Effect of annealing field on asymmetric giant magnetoimpedance profile in Co-based amorphous ribbon

We prepared weak-field annealed amorphous samples in the open air and present the change of giant magnetoimpedance (GMI) profiles as functions of annealing field, H-a. The profile for 0.1 MHz measuring frequency shows two typical peaks in the sample annealed in a field of H-a < 50 mOe. Increasing H-a to 500 mOe, the CMI peak in the region where the applied field is antiparallel to the annealing field decreases with H-a, showing an asymmetric GMI profile. As the annealing field increases over 500 mOe, GMI in the antiparallel field region disappears and a GMI-valve in the parallel field region is revealed due to the exchange coupling of domains in the amorphous core with the unidirectional anisotropy field in a crystalline layer. However, in the sample with H-a of 15 Oe, the GMI peak ill the antiparallel region is observable again. (C) 2000 Elsevier Science B.V. All rights reserved.