Surface magnetoimpedance measurements in soft-ferromagnetic materials

We present an investigation of the surface magnetoimpedance (Z(s)) in ribbo ns of the amorphous alloy Co70.4Fe4.6Si15B10 for a broad range of frequenci es (2 x 10(3) Hz less than or equal to f less than or equal to 2 x 10(8) Hz ) and magnitudes of the ac electrical current (2 mA less than or equal to I -ac less than or equal to 75 mA). The experimental data are interpreted in terms of a theoretical model valid for any value of the skin depth delta, w hich is based on a modification of the currently used semi-infinite sample geometry model, in order to account for a broad range of delta. The shape o f the Z(s) versus applied field (H) curve is mainly determined by the varia tion of delta with H which can attain several orders of magnitude in the fi eld range of the experiments (-3.2 x 10(3) A/m less than or equal to H less than or equal to 3.2 x 10(3) A/m). The results of the model fit very well the Z(s) versus f data using three adjustable parameters: the domain-wall r elaxation time tau (= 250 ns for all values of I-ac used in the experiments ), the transversal magnetic permeability chi(T)(I-ac) and a resonance linew idth Delta H which depend on the value of H.