Magnetoimpedance effect in FINEMET/Ni₈₀Fe₂₀ composite ribbons

Giant magnetoimpedance (GMI) always attracts much attention owing to its importance in promising applications of industrial devices. Although GMI effect of ribbons have been studied for years, the composite ribbons coated with various films are still attractive due to its high sensitivity with respect to the applied magnetic field. Mostly, the magnetic properties were commonly inspected by hysteresis loops, which may not sensitive enough for Fe-based composite ribbons. Herein, by using both hysteresis loops and the GMI measurement, the magnetic properties of the FINEMT ribbons coated with different thickness of Ni₈₀Fe₂₀ film on free side, wheel side and twin sides have been thoroughly analyzed. It is revealed that the shift of anisotropy direction from preferable transverse to partially longitudinal as the film thickness increased, which affected the interaction between ribbon and Ni₈₀Fe₂₀ coating. Moreover, the asymmetric GMI response could be obtained on the ribbon coated with Ni₈₀Fe₂₀ film on single side, whereas the symmetric GMI response was observed for twin-side coating, which indicated the dipole interaction in the composite ribbons. We found that the ribbon with 260 nm Ni₈₀Fe₂₀ film showed the optimized transverse anisotropy, leading to the smallest H_c and the optimal soft magnetic properties. Hence, GMI measurement can be a sensitive alternative tool to investigate dipole interaction, which can be employed to manufacture novel linear GMI sensors and to properly regulate the operation field.