Permeability spectra of Permalloy wires at microwave frequencies

Impedance spectra of soft magnetic wires were measured in the 10 MHz-6 GHz frequency range using a shorted coaxial line in presence of a longitudinal magnetic field. The inner conductor of the line was replaced by a Permalloy wire, 44 or 118 μm in diameter. Permeability spectra have been deduced from impedance measurements using the expression for the skin depth. These spectra show that ferromagnetic resonance occurs in the wire at microwave frequencies. The energy absorption which accompanies this resonance can be used to obtain magnetic field controlled attenuators, which show very little phase shift, as well as magnetic filters