Giant magnetoimpedance, skin depth and domain wall dynamics

Summary form only given, as follows. Giant magnetoimpedance (GMI) has raised a strong interest due to its technological applications in magnetic field and dc current sensors. In this work, a detailed analysis of the impedance response of a typical material (CoFeBSi amorphous wires with high circumferential permeability and low negative magnetostriction) on a wide frequency range, is presented. By using the quasistatic circumferential permeability (actually measured on samples at 100 kHz) the skin depth is calculated, which is larger than the wire diameter for frequencies up to tens of kHz. The analysis of the real and imaginary contributions to impedance in this frequency range is consistent with a magnetization process dominated by domain wall movements. For frequencies higher than the domain wall relaxation, where only the magnetization process is spin rotation, the behavior of impedance can be modeled by means of the general expression based on first order Bessel equations. Impedance calculated in this way, showed a good agreement with experimental results. The domain wall relaxation process was also studied; its unusually large frequency extension can be explained in terms of the Foucault microcurrents generated by the wall movements, which give an additional damping factor.