Effect of AC driving current on magneto-impedance effect

Magneto-impedance (MI) ratio (Delta Z/Z)=Z(H) - Z(H-max)/Z(H-max) has been measured in different materials: amorphous (Fe0.94Co0.06)(72.5)B15Si12.5 wires and Co68.5Mn6.5Si10B15 microwires and nanocrystalline Fe73.5Si13.5B9Nb3Cu1 ribbons, with axial magnetic field H, intensify I, and frequency f, of the AC driving current as the parameters. The common feature of these samples is that they show a peculiar MI effect with a maximum of (Delta Z/Z) at a certain axial magnetic field value, H-m. Dependencies of (Delta Z/Z) and H-m on the AC driving current amplitude I have been observed: H-m decreases with I. The NI ratio can be optimised by means of choosing an adequate value of I. particularly, in the case of microwires, (Delta Z/Z) has a maximum at I = 2.8 mA. The observed effect is explained taking into account the tensor character of magnetic permeability and the circular magnetisation processes. (C) 2000 Elsevier Science S.A. All rights reserved.