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 (4 5 MHz-3 GHz). The impedance is determined through the analysis of the refle ction parameter of a coaxial transmission line, where the inner conductor h as been replaced by the active magnetic material. Two different kinds of sa mples have been used. Glass-coated Go-rich microwires (with a metallic diam eter of 8 mu m), prepared by a modified Taylor technique, art:known to show important microwave radiation absorption. On the other hand, polycrystalli ne HyMu80(R) permalloy wires also exhibit interesting impedance patterns. R esults obtained show a different behavior of the evolution of impedance wit h the magnetic field in the low-frequency range (up to 1 GHz) and for highe r frequencies. In the first case, a negative magneto impedance effect is ob served while when the frequency is higher, the effect becomes positive. Thi s behavior is observed in both kinds of samples analysed, and can be! assoc iated with ferromagnetic resonance phenomena. In the case of HyMu80(R) perm alloy wires, for frequencies higher than 2.5 GHz, the initial behavior (pos itive effect) is recovered. (C) 2000 Elsevier Science S.A. All rights reser ved.