This paper concerns the theoretical and experimental investigation of the magnetoimpedance (MI) effect in amorphous wires in terms of the surface impedance tensor $\hat{\varsigma }.$ Physical concepts of MI and problems of significant practical importance are discussed using the results obtained. The theoretical analysis is based on employing the asymptotic-series-expansion method of solving the Maxwell equations for a ferromagnetic wire with an ac permeability tensor of a general form associated with magnetization rotation. The magnetic-structure-dependent impedance tensor $\hat{\varsigma }$ is calculated for any frequency and external magnetic field, and is not restricted to the case when only strong skin effect is present. This approach allows us to develop a rigorous quantitative analysis of MI characteristics in wires, depending on the type of magnetic anisotropy, the magnitude of dc bias current, and an excitation method. The theoretical model has been tested by comparing the obtained results with experiment. For the sake of an adequate comparison, the full tensor $\hat{\varsigma }$ is measured in CoFeSiB and CoSiB amorphous wires having a circumferential and helical anisotropy, respectively, by determining the $S_{21}$ parameter. In cases when the rotational dynamics is responsible for the impedance behavior, there is a reasonable agreement between the experimental and theoretical results. Such effects as the ac biased asymmetrical MI in wires with a circumferential anisotropy, and the transformation in MI behavior caused by a dc current (from that having a symmetric hysteresis to an asymmetric anhysteretic one) in wires with a helical anisotropy are discussed.

• Received 27 June 2000

DOI:https://doi.org/10.1103/PhysRevB.63.144424