Cryogenic Joule annealing induced large magnetic field response of Co-based microwires for giant magneto-impedance sensor applications

We have presented herein the results of microstructure, surface magnetic domains (SMDs), and giant magneto-impedance (GMI) effect of melt-extracted Co68.15Fe4.35Si12.25B11.25Nb2Cu2 amorphous wires for the first time employed by using a cryogenic Joule annealing (CJA) technique with large DC current amplitude. Compared with the conventional JA method, experimental results indicate that the maximum GMI ratio [Delta Z/Z(0)](max) achieves up to 425% at 8.1 MHz with monotonic increase of the axial magnetic field H-ex up to 6.5 Oe for 300 mA (equal to around 1.06 x 10(6) A/dm(-2)) CJA-ed wire, which is about 75% larger than the [Delta Z/Z(0)](max) for the 100 mA (nearly 3.53 x 10(5) A/dm(-2)) JA-ed microwires. The remarkable features of large and linearly sensitive response field (2.5 similar to 6.5 Oe) and the sensitivity of 99.4%/Oe with higher GMI ratio simultaneously make the CJA tailored melt-extracted microwires promising candidate materials for miniaturized GMI sensors. Another interesting result of GMI profiles of 200 mA (appropriately equal to 7.07 x 10(5) A/dm(-2)) CJA-ed wire show a linear response to H-ex (ranging from 10 to 80 Oe or more), this behavior of GMI curves can be explored to fabricate bi-sensor. Large response field proves to originate from the intensive coupling between the radial stress field and the circumferential magnetic field during CJA process. The effect of outer-shell microstructure and complex SMD for 300 mA CJA-ed microwire is attributed to the fact that liquid nitrogen hinders the evolution of circumferential domain structure to some extent and protects the amorphous structure in the shell region. (C) 2014 AIP Publishing LLC.