GIANT AC MAGNETORESISTANCE IN THE SOFT FERROMAGNET CO70.4FE4.6SI15B10

ac magnetoresistance (MR) measurements performed in thin ribbons of the amorphous soft ferromagnet Co70.4Fe4.6Si15B10 are reported with a longitudinal dc applied magnetic field H varying from 0 to +/- 15 Oe. The dependence of the MR with the frequency f of the measuring ac current was investigated for 0.4 less-than-or-equal-to f less-than-or-equal-to 100 kHz. No significant frequency dependence in the resistivity rho for H= 0 and H = +/- 15 Oe was found. For intermediate values of H, rho(H) presents a peak in H which increases linearly in frequency. The MR peak in H at room temperature varies from typical values of 0.13% in the low-frequency range to a giant value of 27% at 100 kHz. Two possible sources for the frequency dependence of the magnetoresistance in amorphous alloys are discussed.