  A model describing the asymmetric giant magnetoimpedance (GMI) in
field-annealed amorphous ribbons is proposed. It is assumed that the ribbon
consists of an inner amorphous core and surface hard magnetic crystalline
layers. The model is based on a simultaneous solution of linearizied Maxwell
equations and Landau-Lifshitz equation. The coupling between the surface layers
and the amorphous core is described in terms of an effective bias field.
Analytical expressions for the frequency and field dependences of the ribbon
impedance are found. The calculated dependences are in a qualitative agreement
with results of experimental studies of the high-frequency asymmetric giant GMI
in field-annealed amorphous ribbons.
