Annealing temperature dependence of permeability spectra and asymmetrical giant magnetoimpedance in Co-based amorphous ribbon

Abstract

The permeability spectra and giant magnetoimpedance (GMI) profiles have been measured as a function of annealing temperature, T-a in field-annealed Co-based amorphous ribbon. The permeability spectra show the superposition of two dispersions of Debye type for T(a)less than or equal to 200 degrees C. As T-a increases over 250 degrees C, the low frequency dispersion begins to decrease, and eventually disappears for T(a)greater than or equal to 350 degrees C due to the exchange coupling with the bias field formed in surface crystalline layer. However, the high frequency dispersion increases with T-a up to 350 degrees C and then becomes nearly constant. The GMI profile measured at 0.1 MHz shows a one peak in the samples of T(a)less than or equal to 300 degrees C. As T-a increases over 350 degrees C, the GMI-valve is revealed due to the influence of bias field on wall motion. As the T-a increases over 450 degrees C, the asymmetric two peaks of GMI profile are shown instead of the GMI valve due to the damping of wall motion after the crystallization. (C) 2000 American Institute of Physics. [S0021-8979(00)20808-6].