Combined current-modulation annealing induced enhancement of giant magnetoimpedance effect of Co-rich amorphous microwires

We report on a combined current-modulation annealing (CCMA) method, which integrates the optimized pulsed current (PC) and DC annealing techniques, for improving the giant magnetoimpedance (GMI) effect and its field sensitivity of Co-rich amorphous microwires. Relative to an as-prepared Co68.2Fe4.3B15Si12.5 wire, CCMA is shown to remarkably improve the GMI response of the wire. At 10MHz, the maximum GMI ratio and its field sensitivity of the as-prepared wire were, respectively, increased by 3.5 and 2.28 times when subjected to CCMA. CCMA increased atomic order orientation and circumferential permeability of the wire by the co-action of high-density pulsed magnetic field energy and thermal activation energy at a PC annealing stage, as well as the formation of uniform circular magnetic domains by a stable DC magnetic field at a DC annealing stage. The magnetic moment can overcome eddy-current damping or nail-sticked action in rotational magnetization, giving rise to a double-peak feature and wider working field range (up to +/- 2 Oe) at relatively higher frequency (f >= 1 MHz). (C) 2014 AIP Publishing LLC.