Surface impedance tensor in amorphous wires with helical anisotropy: Magnetic hysteresis and asymmetry

Abstract

This article concerns the investigation of the magnetic behavior of the surface impedance tensor final_sigmâ in CoSiB amorphous wires having a residual torsion stress and a helical anisotropy. The full tensor final_sigmâ involving three different components is found by measuring the S21 parameter at a required excitation with a Hewlett-Packard network/spectrum analyzer at MHz frequencies. In general, the impedance plots versus axial magnetic field Hex exhibit a hysteresis related to that for the case of static magnetization. The diagonal components of final_sigmâ (longitudinal final_sigmazz and circular final_sigmaφφ) show a sharp peak in a narrow field interval where the domain walls form and contribute to the ac magnetization dynamics. This peak is not seen for the off-diagonal component final_sigmazφ (final_sigmaφz) since the existence of the domain structure suppresses it. Applying a dc bias current results in a gradual transition to a nonhysteretic asymmetrical behavior with an enhanced sensitivity. The portions of the experimental plots associated with the rotational dynamic process are in qualitative agreement with the theory based on a single-domain model.