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

This article concerns the investigation of the magnetic behavior of the sur face impedance tensor <(<sigma>)over cap> in CoSiB amorphous wires having a residual torsion stress and a helical anisotropy. The full tensor <(<sigma >)over cap> involving three different components is found by measuring the S-21 parameter at a required excitation with a Hewlett-Packard network/spec trum analyzer at MHz frequencies. In general, the impedance plots versus ax ial magnetic field H-ex exhibit a hysteresis related to that for the case o f static magnetization. The diagonal components of <(<sigma>)over cap> (lon gitudinal sigma (z phi) and circular sigma (phi phi)) show a sharp peak in a narrow field interval where the domain walls form and contribute to the a c magnetization dynamics. This peak is not seen for the off-diagonal compon ent sigma (z phi) (sigma (phiz)) since the existence of the domain structur e 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-doma in model. (C) 2001 American Institute of Physics.