Optimization of Magnetic Properties and Giant Magnetoimpedance Effect in Nanocrystalline Microwires

We studied giant magnetoimpedance (GMI) effect, magnetic, and magneto-optic properties of Finemet-type FeCuNbSiB microwires. We observed that GMI effect and magnetic softness of glass-coated microwires produced by the Taylor-Ulitovsky technique can be tailored either controlling magnetoelastic anisotropy of as-prepared FeCuNbSiB microwires or controlling their structure either by heat treatment or changing the fabrication conditions. We observed considerable magnetic softening of studied microwires after annealing. This magnetic softening correlates with the devitrification of amorphous samples. Amorphous Fe-rich microwires exhibited low GMI effect (GMI ratio below 1 %). Considerable enhancement of the GMI effect (GMI ratio up to 100 %) has been observed in heat-treated microwires with nanocrystalline structure. Some of as-prepared Fe-rich magnetic microwires exhibited nanocrystalline structure and GMI ratio up to 45 %. The magneto-optical study demonstrated the existence of helical surface magnetic structure in the as-prepared microwires.