Several routes allowing 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, giant magnetoimpedance (GMI) effect and fast domain wall (DW) propagation. 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 low GMI ratio, stress-annealing and combined stress-annealed 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 has been thoroughly analyzed paying attention on the influence of magnetoelastic, induced, and magnetocrystalline anisotropies. Minimization magnetoelastic anisotropy by choosing low magnetostrictive compositions or by appropriate annealing is suitable route to optimize 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 structure 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, like, magnetic hardening, Giant Magnetoresistance (GMR) or Magnetocaloric (MCE) effects. Magnetic and transport properties of crystalline microwires are influenced by the structure and chemical composition. Actual and prospective application scenarios of magnetic microwires and future developments are briefly overviewed.

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In this work, we were able to produce Co2FeSi Heusler alloy glass-covered microwires with a metallic nucleus diameter of about 4,4 µm and total sample diameter of about 17,6 μm by the Taylor–Ulitovsky Technique. This low cost and single step fabrication process allowed the preparation of up to kilometers long glass-coated microwires starting from a few grams of high purity inexpensive elements (Co, Fe and Si), for a wide range of applications. From the X-ray diffraction, XRD, analysis of the metallic nucleus, it was shown that the structure consists of a mixture of crystalline and amorphous phases. The single and wide crystalline peak was attributed to a L21 crystalline structure (5.640 Å), with a possible B2 disorder. In addition, nanocrystalline structure with an average grain size, Dg = 17.8 nm, and crystalline phase content of about 52% was obtained. The magnetic measurements indicated a well-defined magnetic anisotropy for all ranges of temperature. Moreover, soft magnetic behavior was observed for the temperature measuring range of 5–1000 K. Strong dependence of the magnetic properties on the applied magnetic field and temperature was observed. Zero field cooling and field cooling magnetization curves showed large irreversibility magnetic behavior with a blocking temperature (TB= 205 K). The in-plane magnetization remanence and coercivity showed quite different behavior with temperature, due to the existence of different magnetic phases induced from the internal stress created by the glass-coated layer. Moreover, a high Curie temperature was reported (Tc ≈ 1059 K), which predisposes this material to being a suitable candidate for high temperature spintronic applications.

Herein, detailed studies on the influence of stress annealing on the magnetic softness and giant magnetoimpedance (GMI) ratio of Co69.2Fe3.6Ni1B12.5Si11Mo1.5C1.2 glass‐coated microwires are provided. As‐prepared microwire presents linear hysteresis loops, moderate GMI ratio with double‐peak magnetic field dependence and low coercivity (4 A m−1), typically observed for wires with transverse magnetic anisotropy. However, after conventional annealing magnetic hardening and transformation of linear hysteresis loop into rectangular with coercivity about 90 A m−1 is surprisingly observed. It is shown that stress annealing allows preventing magnetic hardening and remarkably improving GMI ratio. Properly stress‐annealed samples present better magnetic softness: almost unhysteretic loops with coercivity about 2 A m−1 and magnetic anisotropy field about 35 A m−1. Observed stress‐annealing‐induced anisotropy is affected by the tensile stresses, applied during annealing and by the annealing temperature. From the frequency dependence of the maximum GMI ratio, the optimum frequency ranges for as‐prepared and stress‐annealed samples are determined. The observed stress‐annealing‐induced magnetic anisotropy and associated changes in magnetic properties and GMI effect are discussed in terms of internal stresses relaxation and related modification of the magnetostriction coefficient, “back stresses,” structural anisotropy, redistribution of internal stresses, and change of spatial distribution of magnetic anisotropy.