High frequency impedance spectra of soft amorphous fibers

Giant magnetoimpedance (GMI) spectra of soft amorphous magnetic fibers, measured in the 1 kHz-1.2 GHz frequency range, and GMI responses, measured in the field range of +/-120 Oe, have reinforced the assumption that linear giant magnetoimpedance and ferromagnetic resonance (FMR) have the same physical origin. The samples, NiCo-rich, CoFe-rich, and Metglas-type fibers, 30-40 mu m in diameter, were cast by melt extraction. Their impedance has been measured up to 13 MHz, in the presence of a magnetic field, using an impedance analyzer. These measurements have been extended up to 1.2 GHz by using a network analyzer. The reflection coefficient of a shorted coaxial line whose inner conductor was replaced by a magnetic fiber was measured, and the input impedance per unit length of this line was then calculated. The two impedances above are equivalent and their spectra show a behavior associated with FMR: the real part of the impedance peaks at a frequency where the imaginary part passes through zero. (C) 1997 American Institute of Physics.