Magneto-impedance effect in amorphous wires

A commercially amorphous FeCoSiB wire was used for the magneto-impedance measurement. This effect includes a sensitive change (as much as 60%) in a high frequency wire voltage by an applied d.c. magnetic field and is thus a high frequency analogue of giant magneto-resistance. Some samples were annealed at a temperature slightly below its Curie point, and cooled in a transverse or longitudinal field. The frequency of the probe current was from 10 kHz to 10 MHz. At relatively low frequencies the magneto-impedance (MI) is mostly inductive, at relatively high frequencies it is resistive and a crossover could be defined at a characteristic frequency f0. We have studied the variation of this frequency with annealed conditions, and we have found that for frequencies upward f0 the MI effect is dominated by the skin depth effect.