Study of the complex permeability of amorphous wires using microwave impedance spectroscopy

We have measured (10 MHz-6 GHz) the magnetoimpedance of ferromagnetic amorphous wires placed as internal conductors in shorted coaxial lines. Three types of materials have been investigated: CoFeSiB wires from Unitika (Japan), cast by rapid quenching in water, and NiCoFeSiBMn and CoFeSiNbB wires from MXT (Canada), cast by melt extraction. In order to investigate magnetic properties, we used a complex permeability formalism directly obtained from impedance by means of a transformation which leads to an exchange in components from real to imaginary and vice-versa. From the analysis of Cole-Cole plots of the relative permeability, ferromagnetic resonance was identified as the magnetization process occurring when an axial dc magnetic field of several hundred oersteds was applied to the line. An equivalent circuit of the magnetic wire was used to demonstrate that the field variation of the inverse of the equivalent resistance was quite similar to those of the line width vs resonance frequency ratio and of the maximum of the imaginary part of the relative permeability