Giant magnetoimpedance effect in soft and ultrasoft magnetic fibers

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Abstract
Soft NiFe‐Permalloy fibers and ultrasoft NiCo‐based amorphous fibers, having a circular cross section with 30–40 μm in diameter, have been cast by melt extraction. The fibers have been driven by a sinusoidal current with 20 mApp constant amplitude and frequencies from 0.1 to 100 MHz. Both longitudinal and transverse giant magnetoimpedance effects have been observed in these fibers. The longitudinal GMI effect at 30 MHz was 60% in ultrasoft (NiCo)70FeSiBMn fibers for a saturating field of about 7 kA/m. The same effect was found at 10 MHz frequency for Permalloy fibers for a larger saturating field (20 kA/m). The transverse GMI effect was smaller (≊35% for NiCo and ≊20% for NiFe), and showed a maximum at low frequency (3 MHz). The magnetic field responses of the fibers are quadratic. An inverse effect of 10%–30% was observed for both types of fibers in longitudinal as well as in transverse field responses at high current frequency and low field strength. All of the observed effects could prove to be very useful for a new generation of high‐sensitivity magnetic field sensors.