Tailoring GMI effect in Co-rich glass coated microwires by Joule heating

Abstract

The dependence of magnetoimpedance ratio, ΔZ/Z = {[Z(H)-Z(H_max)]/Z(H_max)}.100%, on the axial magnetic field of soft magnetic Co₆₇Fe_3.85Ni_1.45B_11.5Si_14.5Mo_1.7glass coated amorphous microwires has been investigated in the frequency range 1 - 30 MHz, for the driving current amplitudes 0.75 - 5 mA, and at the maximum axial DC-field of 8 kA/m. In the as-prepared sample, maximum GMI ratio, ΔZ/Z_max≈380%, has been observed at the highest used frequency (30 MHz). It has, however, been shown, that Joule heating enables to enlarge the ΔZ/Z_max ratio up to 500%. A strong dependence of ΔZ/Z_max on annealing time, frequency and amplitude of the driving current has also been observed. The results of the GMI measurements, presented as a function of the annealing time with the frequency and current amplitude as the parameters, showed an increase of the anisotropy field with an increase of the annealing time and temperature. The observed dependencies have been interpreted in terms of stress relaxation and changes of the magneto-elastic anisotropy induced by the Joule heating.