Advanced functional magnetic microwires for technological applications

Abstract

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.

Fabrication and Magneto-Structural Properties of Co2-Based Heusler Alloy Glass-Coated Microwires with High Curie Temperature

“…The repetition of the melting process was done several times to improve homogeneity of the alloy. Magnetic glass-coated microwires were fabricated by the Taylor-Ulitovsky technique, which consisted of drawing and casting directly from the melted Co 50 Fe 25 Si 25 alloy, as described in detail elsewhere [33,[36][37][38][51][52][53][54][55][56]. Briefly, an ingot was heated above its melting point by a high frequency inductor, then a glass capillary was formed, which was filled with molten alloy, drawn out and wound onto a rotating pick-up bobbin [33,35,36].…”

“…The Taylor-Ulitovsky technique, involving rapid melt quenching, is suitable for preparation of thin glass-coated magnetic microwires (G-CMMWs). This technique offers low cost and fast production of thin metallic microwires, without the need for additional dimensionality reduction processes or long thermal treatments [32][33][34][35][36][37][38]. Recently, rapidly quenched low-dimensional nanocrystalline and amorphous materials gained special interest, due to their promising mechanical properties, excellent magnetic properties and magneto-transport properties [35,36,[39][40][41][42].…”

“…Amorphous and nanocrystalline rapidly quenched materials can present unique combinations of magnetic properties, such as extremely fast domain wall propagation or giant magnetoimpedance effect [36,37,[39][40][41][42][43][44]. One of the most relevant factors of these rapid quenching materials is the possibility to tailor the microstructure of the quenched alloys by controlling different parameters, such as the quenching rate, the chemical composition and the melting temperature of the selected alloy, and its phase diagram [35].…”

“…One of the most relevant factors of these rapid quenching materials is the possibility to tailor the microstructure of the quenched alloys by controlling different parameters, such as the quenching rate, the chemical composition and the melting temperature of the selected alloy, and its phase diagram [35]. One of the main advantages of this technology is that it is suitable for fast (hundreds of meters per minute) fabrication of rather long and continuous metallic microwires (up to several kilometers long) with the widest possible diameter range (by four orders of magnitude, i.e., from 0.1 to 100 µm), covered with insulating and flexible glass-coating [28,31,[33][34][35][36][43][44][45]. In addition, the existence of flexible, thin, highly transparent and insulating glass coating works on improving mechanical and biocompatibility properties, which opens the door for the biomedical application of the G-CMMWs [46][47][48].…”

“…In addition, the existence of flexible, thin, highly transparent and insulating glass coating works on improving mechanical and biocompatibility properties, which opens the door for the biomedical application of the G-CMMWs [46][47][48]. Finally, by the single-step method, with a high quenching rate, it is possible to produce microwires from Heusler alloys with single crystalline phase and well-defined magnetic anisotropy [4,7,[33][34][35][36]49,50]. Therefore, the Co 2 -based Heusler G-CMMWs represent a promising smart metamaterial for multi-functional application for a new generation of spintronic devices.…”