Optimization of magnetic properties and GMI effect of Thin Co-rich Microwires for GMI Microsensors

Abstract

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.

Optimization of Magnetic Properties of Magnetic Microwires by Post-Processing

“…Thus, in certain stress-annealing conditions, Co 68.7 Fe 4 Ni 1 B 13 Si 11 Mo 2.3 microwires with rectangular hysteresis loops and extremely low coercivity of about 1A/m can be obtained (see Figure 21) [102]. In the case of Co-based microwires higher annealing temperature, time or stresses are required to prevent magnetic hardening associated with relaxation of internal stresses related to glass-coating [42,43,101]. As can be observed in Figures 19 and 20, for extended range of Tann, tann or σm, stressannealed Co-rich microwires present rectangular hysteresis loops.…”

Magnetoimpedance Response and Field Sensitivity in Stress-Annealed Co-Based Microwires for Sensor Applications

“…However, it has been recently noticed that conventional annealing produces a considerable magnetic hardening in different Co-rich microwires with vanishing λ s -values [32,33]. Such magnetic hardening is a detriment to the GMI performance [27,32,33]. Nevertheless, we have recently observed that stress-annealing can be successfully employed to induce a transverse anisotropy and hence improve the GMI effect of magnetic microwires [27,32,33].…”

“…In this regard, at a fixed composition and geometry (metallic nucleus diameter and glass-coating thickness) the magnetic anisotropy can be fine-tuned either by the internal stresses relaxation (usually by conventional annealing) or by inducing magnetic anisotropy [27,32]. However, it has been recently noticed that conventional annealing produces a considerable magnetic hardening in different Co-rich microwires with vanishing λ s -values [32,33]. Such magnetic hardening is a detriment to the GMI performance [27,32,33].…”

“…Such magnetic hardening is a detriment to the GMI performance [27,32,33]. Nevertheless, we have recently observed that stress-annealing can be successfully employed to induce a transverse anisotropy and hence improve the GMI effect of magnetic microwires [27,32,33].…”

Optimization of Magnetic Properties of Magnetic Microwires by Post-Processing

“…In the case of Co-based microwires higher annealing temperature, time or stresses are required to prevent magnetic hardening associated to relaxation of internal stresses related to glass-coating [42,43,101]. As can be observed in Figures 19 and 20, for extended range of Tann, tann or σm, stress-annealed Co-rich microwires present rectangular hysteresis loops.…”