Abstract

Measurements of microwave magnetoimpedance of melt-extracted Fe-rich amorphous wires are presented. These wires were simultaneously submitted to a microwave electromagnetic wave propagating at the wire surface, Joule heating and circumferential static magnetic field. This field is generated by a DC electric current. owing through the wire with maximum strength of 90 mA in order not to reach the recrystallization temperature of the amorphous alloy. The impedance was measured up to 6 GHz using a technique based on the s-parameters measurement of a custom-designed coaxial line by means of a vectorial network analyzer. The real part of the impedance spectra we obtained show peaks, which characterize the magnetic losses occurring in the amorphous material. These peaks shift toward lower frequency for stronger DC currents. Theoretically, these results can be accounted for by the fact that the peaks frequency represents the ferromagnetic resonance occurring in the magnetic material. Its magnitude depends on the saturation magnetization. Since this magnetization decreases with temperature following the Curie law, the resonance frequency also decreases and the impedance peaks shift towards lower frequency. (c) 2007 Published by Elsevier B.V.