Optimization of the high-frequency magnetoimpedance response in melt-extracted Co-rich microwires through novel multiple-step Joule heating

TL;DR

This study demonstrates that multi-step Joule annealing significantly enhances the high-frequency GMI response and magnetic sensitivity of Co-rich microwires, with potential applications in biomedical sensing.

Contribution

The paper introduces a novel multi-step Joule annealing process that improves GMI performance in melt-extracted Co-rich microwires, surpassing previous methods.

Findings

GMI ratio increased up to 760% after annealing.

Field sensitivity improved to 925%/Oe.

Surface magnetic domain structures were optimized.

Abstract

The optimization of high frequency giant magnetoimpedance (GMI) effect and its magnetic field sensitivity in melt-extracted Co69.25Fe4.25Si13B12.5Nb1 amorphous microwires, through a multi-step Joule annealing (MSA) technique, was systematically studied. The surface morphology, microstructure, surface magnetic property, and high frequency GMI response of the Co-rich microwires were explored using scanning electron microscopy (SEM), magneto-optical Kerr effect (MOKE) magnetometry, transmission electron microscopy (TEM), and impedance analyzer, respectively. An initial dc current (idc) of 20 mA, which was then increased by 20 mA at every time-step (10 min) up to 300 mA, was applied to the microwires. The MSA of 20 mA to 100 mA remarkably improved the GMI ratio and its field sensitivity up to 760% (1.75 time of that of the as-prepared), and 925%/Oe (more than 17.92 times of that of the as-prepared) at an operating frequency of 20 MHz, respectively. Our study indicates that the MSA technique can enhance the microstructures and the surface magnetic domain structures of the Co-rich magnetic microwires, giving rise to the GMI enhancement. This technique is suitable for improving the GMI sensitivity at small magnetic fields, which is highly promising for biomedical sensing and healthcare monitoring.