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

Abstract

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 [ΔZ/Z0]max achieves up to 425% at 8.1 MHz with monotonic increase of the axial magnetic field Hex up to 6.5 Oe for 300 mA (equal to around 1.06 × 106 A/dm−2) CJA-ed wire, which is about 75% larger than the [ΔZ/Z0]max for the 100 mA (nearly 3.53 × 105 A/dm−2) JA-ed microwires. The remarkable features of large and linearly sensitive response field (2.5 ∼ 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 × 105 A/dm−2) CJA-ed wire show a linear response to Hex (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.

Influence of microstructure evolution on GMI properties and magnetic domains of melt-extracted Zr-doped amorphous wires with accumulated DC annealing

“…Notch-defects may be resulted from the residual stress and distribution of magnetic charge, while antinotch-defects region (II) of Fig. 9c may be induced by the existence of zirconium atoms which are favor to form atomic clusters [28]. The defects existence on surface circumferential magnetic domains will reduce the circumferential permeability, which is provide closely associating with the GMI effect [29].…”

In-situ microwave characterization of ferromagnetic microwires-filled polymer composites: A mini review

“…Naturally it is realized that their microwave response could be more controllable and sensitive to external stimuli providing moderate wire treatment is done before embedding into the matrix. Recently, it has been reported that several emerging techniques including the combined current-modulation annealing (CCMA) [34], twin zone Joule annealing [35] and cryogenic Joule annealing [36] can significantly enhance the GMI effect and field sensitivity of Co-based microwires. Hence we believe that enhanced field/stress/current sensitivity in addition to other unique physics will be realized by performing such tailoring techniques to microwires prior to incorporating them into polymer context.…”

Domain Transformation and MI of Melt-extracted Co68.15Fe4.35Si12.25B13.25Nb1Cu1 Microwires by Cryogenic Joule Annealing

“…The result of the coupling effect leads to the unique surface domain structure of the microwire. The phenomenon that the response of the ΔX/X (%) obviously hysteretic to the ΔZ/Z (%) nearly 1.2 Oe is resulting from the crystallization of inner part due to the over Joule heat under large current while the outer-shell part keeping amorphous microstructure owing to the protection of liquid nitrogen 11 . In this case, the induced circumferential fields observed for the ΔX/X (%) curves after 300 mA CJA appear a large platform without sharp peak which corresponding to the response field H ex .…”

“…Meanwhile, the Joule heat generated by CJA is enough to meet the atoms redistribution or crystallization 13 . However, the cool role of the liquid nitrogen around the microwire protects the surface amorphous microstructure against crystallization or oxidation during CJA process 11 . Moreover, it restrains the formation of surface domain rotation.…”