VERY LARGE MAGNETO-IMPEDANCE IN AMORPHOUS SOFT FERROMAGNETIC WIRES (INVITED)

Changes in the impedance, approximate to 600%/Oe, at axial fields less than 1 Oe have been observed in the presence of a 90 kHz, few mA curr ent through a soft, nearly zero magnetostrictive wire. In this 125 mu m diameter CoFeSiB amorphous wire we observe a total change of 160% at the maxima of the impedance in de fields less than 2 Oe. A systematic study of the role of induced anisotropy in the axial, circumferential , and helical directions on the magneto-impedance shows that the large st effect is seen in the wire annealed to obtain circumferential easy axis using a 15 mA ac current passing through it. Both the axial hyste resis loops and the observed I-V characteristics reflect the induced a nisotropies. The observed dependence of the inductance change on the t ype of the anisotropy induced in these wires can be modeled in terms o f an interplay between the induced anisotropy, reversing ac field, and the axial de field.