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.
The influence of magnetic anisotropy, post-processing conditions, and defects on the domain wall (DW) dynamics of amorphous and nanocrystalline Fe-, Ni-, and Co-rich microwires with spontaneous and annealing-induced magnetic bistability has been thoroughly analyzed, with an emphasis placed on the influence of magnetoelastic, induced and magnetocrystalline anisotropies. Minimizing magnetoelastic anisotropy, either by the selection of a chemical composition with a low magnetostriction coefficient or by heat treatment, is an appropriate route for DW dynamics optimization in magnetic microwires. Stress-annealing allows further improvement of DW velocity and hence is a promising method for optimization of DW dynamics in magnetic microwires. The origin of current-driven DW propagation in annealing-induced magnetic bistability is attributed to magnetostatic interaction of outer domain shell with transverse magnetization orientation and inner axially magnetized core. The beneficial influence of the stress-annealing on DW dynamics has been explained considering that it allows increasing of the volume of outer domain shell with transverse magnetization orientation at the expense of decreasing the radius of inner axially magnetized core. Such transverse magnetic anisotropy can similarly affect the DW dynamics as the applied transverse magnetic field and hence is beneficial for DW dynamics optimization. Stress-annealing allows designing the magnetic anisotropy distribution more favorable for the DW dynamics improvement. Results on DW dynamics in various families of nanocrystalline microwires are provided. The role of saturation magnetization on DW mobility improvement is discussed. The DW shape, its correlation with the magnetic anisotropy constant and the microwire diameter, as well as manipulation of the DW shape by induced magnetic anisotropy are discussed. The engineering of DW propagation through local stress-annealing and DW collision is demonstrated.
Magnetic microwires can present excellent soft magnetic properties and a giant magnetoimpedance effect. In this paper, we present our last results on the effect of postprocessing allowing optimization of the magnetoimpedance effect in Co-rich microwires suitable for magnetic microsensor applications. Giant magnetoimpedance effect improvement was achieved either by annealing or stress-annealing. Annealed Co-rich presents rectangular hysteresis loops. However, an improvement in magnetoimpedance ratio is observed at fairly high annealing temperatures over a wide frequency range. Application of stress during annealing at moderate values of annealing temperatures and stress allows for a remarkable decrease in coercivity and increase in squareness ratio and further giant magnetoimpedance effect improvement. Stress-annealing, carried out at sufficiently high temperatures and/or stress allowed induction of transverse magnetic anisotropy, as well as magnetoimpedance effect improvement. Enhanced magnetoimpedance ratio values for annealed and stress-annealed samples and frequency dependence of the magnetoimpedance are discussed in terms of the radial distribution of the magnetic anisotropy. Accordingly, we demonstrated that the giant magnetoimpedance effect of Co-rich microwires can be tailored by controlling the magnetic anisotropy of Co-rich microwires, using appropriate thermal treatment.
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