Study of magneto impedance effect in the microwave frequency range for soft magnetic wires and microwires

The field-induced change of the impedance of different magnetic samples has been investigated in a wide frequency range, up to the microwave region (45 MHz-3 GHz). The impedance is determined through the analysis of the reflection parameter of a coaxial transmission line, where the inner conductor has been replaced by the active magnetic material. Two different kinds of samples have been used. Glass-coated Go-rich microwires (with a metallic diameter of 8 mu m), prepared by a modified Taylor technique, art:known to show important microwave radiation absorption. On the other hand, polycrystalline HyMu80(R) permalloy wires also exhibit interesting impedance patterns. Results obtained show a different behavior of the evolution of impedance with the magnetic field in the low-frequency range (up to 1 GHz) and for higher frequencies. In the first case, a negative magneto impedance effect is observed while when the frequency is higher, the effect becomes positive. This behavior is observed in both kinds of samples analysed, and can be! associated with ferromagnetic resonance phenomena. In the case of HyMu80(R) permalloy wires, for frequencies higher than 2.5 GHz, the initial behavior (positive effect) is recovered. (C) 2000 Elsevier Science S.A. All rights reserved.