Chapter 18 - Advanced functional magnetic microwires for magnetic sensors suitable for biomedical applications

Abstract

Several routes allowing the development of low-cost magnetic microwires coated by flexible, insulating, and biocompatible glass coating suitable for biomedical applications, with tunable functional (magnetic, mechanical, corrosive) properties are overviewed. Microwires prepared from immiscible Co–Cu alloys after appropriate annealing present substantial giant magnetoresistance effect. Additionally, as-prepared and annealed CoxCu100−x microwires present Kondo-like behavior manifested as resistivity minimum. Amorphous microwires can present excellent soft magnetic properties and giant magnetoimpedance (GMI) effect. High GMI effect, obtained even in as-prepared Co-rich microwires, can be further improved by appropriate thermal treatment (including conventional annealing, stress annealing, and Joule heating). Fe-rich microwires exhibit low GMI ratio in as-prepared microwires. Magnetic softening and GMI effect improvement are observed in Finemet-type Fe–Cu–Nb–Si–B microwires related to nanocrystallization. Stress annealing and combined stress annealed followed by conventional furnace annealing allow remarkable (more than an order of magnitude) GMI improvement in amorphous Fe-rich microwires. Finally, several biomedical applications of magnetic microwires, including magnetic hyperthermia and biomagnetometry, are provided.