Advanced functional magnetic microwires for technological applications

Abstract

Abstract Several routes allowing the development of low-cost magnetic microwires coated by insulating, flexible, and biocompatible glass coating with tunable magnetic properties are overviewed. Amorphous microwires can present excellent magnetic softness, the giant magnetoimpedance (GMI) effect, and fast domain wall (DW) propagation. A high GMI effect, obtained even in as-prepared Co-rich microwires, can be further improved by appropriate heat treatment (including conventional annealing, stress-annealing, and Joule heating). Although as-prepared Fe-rich amorphous microwires exhibit a low GMI ratio, stress-annealing and combined stress-annealing followed by conventional furnace annealing allow substantial GMI ratio improvement (more than an order of magnitude). Magnetic softening and GMI effect improvement related to nanocrystallization are observed in Finemet-type Fe-rich microwires. The DW dynamics of amorphous and nanocrystalline Fe, Co, and Ni-based microwires with spontaneous and annealing-induced magnetic bistability are thoroughly analyzed, paying attention to the influence of magnetoelastic, induced, and magnetocrystalline anisotropies. Minimizing the magnetoelastic anisotropy by choosing low magnetostrictive compositions or by appropriate annealing is a suitable route to optimize the DW dynamics in magnetic microwires. Further DW dynamics can be achieved by stress annealing, allowing a more favorable distribution of magnetic anisotropy. Single DW dynamics in microwires with nanocrystalline structures is analyzed. Current-driven DW dynamics is observed in Co-rich microwires with annealing-induced magnetic bistability. Crystalline magnetic microwires can present various versatile properties, such as magnetic hardening, the giant magnetoresistance (GMR) effect or the magnetocaloric effect (MCE). Magnetic and transport properties of crystalline microwires are influenced by structure and chemical composition. Actual and prospective application scenarios of magnetic microwires and future developments are briefly overviewed.