Asymmetric Magnetoimpedance Research Articles

Asymmetric off-diagonal magnetoimpedance in field-annealed amorphous ribbons: Analysis of bias current effect

The influence of bias current on the asymmetric off-diagonal magnetoimpedance in field-annealed amorphous ribbons is studied. It is assumed that the ribbon consists of an amorphous bulk and two surface hard magnetic crystalline layers appearing after the annealing. The off-diagonal magnetoimpedance is calculated in the framework of the quasi-static approximation. Without the bias current, the asymmetry in the field dependence of the off-diagonal impedance is related to the exchange coupling between the surface layers and amorphous phase. In the presence of the bias current, the asymmetry results from the interaction between the field induced by the bias current and the exchange coupling bias field. It is shown that the bias current affects significantly the field dependence of the off-diagonal impedance.

CoFeB-Cu layered film with crossed anisotropy for asymmetrical magnetoimpedance

This paper reports experimental results on sensitive (up to 25%/Oe) asymmetric magnetoimpedance (AMI) in magnetic/metallic multilayers with crossed anisotropy, excited by a sinusoidal current (1-100 MHz) biased with a dc current. The film structure having two outer magnetic layers Co/sub 70.2/Fe/sub 7.8/B/sub 22/ and Cu inner lead is made on a glass substrate using dc sputtering. Each layer thickness is 0.5/spl mu/m. The magnetic anisotropy in the upper film is crossed with respect to that in the lower one, which is achieved by current annealing in a longitudinal magnetic field. The AMI characteristics are found by measuring the S/sub 11/ microwave parameter using a HP8753 spectrum analyzer. The asymmetric behavior of the impedance is more pronounced at relatively low frequencies of about a few megahertz where the impedance-field characteristics are caused by domain-wall dynamics. The obtained results present a very good compromise on size, sensitivity, and linearity.

Stress-induced asymmetric magneto-impedance in melt-extracted Co-rich amorphous wires

The longitudinal magnetization of Co-rich melt-extracted wires has been investigated using magneto-impedance (MI) spectroscopy at variable longitudinal field (−4 to +4 Oe) and constant frequency (10 MHz). During the experiment, the wire was submitted to tensile stresses ranging from 0 to 500 MPa. Magnetoelastic effects in the negative magnetostriction wire and the initial saturation of the wire material produce an asymmetrical MI response of the wire with respect to the applied DC magnetic field. This response shows a very steep linear region crossing the H=0 axis. Thus, a melt-extracted wire under stress can be used as an internally biased sensing element to detect very low magnetic fields with a sensitivity as high as 300%/Oe.

Asymmetric characteristics of magnetoimpedance in amorphous Fe 77.5Si 7.5B 15 wire

The magnetoimpedance (MI) are measured as functions of measuring frequency, DC-biased current and torsion angle of −50° to +50° on Fe 77.5Si 7.5B 15 amorphous wire. The MI profile for 1 MHz measuring frequency, due to the wall motion in circular direction, shows one symmetric peak for the positive torsion angle, where counterclockwise direction is taken as positive. However, for the negative angle up to 30°, two asymmetric peaks are revealed for decreasing field and one peak for increasing field, and then become one peak for the further angle. The shape of asymmetric MI profile changes sensitively with the direction of DC-biased current for negative torsion. However, there is no change with current for positive torsion.