• annealing;
  • giant magneto-impedance;
  • magnetic domains;
  • magnetic field sensors;
  • microstructure;
  • microwires

A systematic study of magnetic domains, microstructure and giant magneto-impedance (GMI) effect of melt-extracted Co68.15Fe4.35Si12.25B13.75Nb1Cu0.5 amorphous wires annealed by d.c. current ranging from 30 mA (1.06 × 105 A dm−2) to 200 mA (7.07 × 105 A dm−2) was conducted. Experimental results indicate that the wire annealed at 80 mA (2.83 × 105 A dm−2) for 180 s has improved maximum GMI ratio and field sensitivity response of 364.7% and 7.36% (A m−1), respectively. This is attributed to the formation of the well-defined circumferential domain structure observed by a magnetic force microscopy (MFM) and the precipitation of fine nanocrystallines identified with high-resolution transmission electron microscopy (HRTEM). A twin-working zone of 0–0.5 and 3–15 Oe is also identified for the annealed wires at 80 mA, which remarkable feature combined with the ever large sensitivity make the d.c. current tailored melt-extraction wires promising candidate materials for field sensing applications.