Co-based Glass-coated Microwires Research Articles

Vol4 num4-16 Magnetic properties and applications of glass-coated ferromagnetic microwires

The impact of post-processing on soft magnetic properties and the giant magnetoimpedance (GMI) effect of Fe- and Co-based glass-coated microwires is evaluated. A remarkable improvement of magnetic softness and GMI effect is observed in Fe-rich glass-coated microwires subjected to stress annealing. Frequency dependence of GMI ratio of stress-annealed Fe-rich microwires has been discussed considering frequency dependence of the skin penetration depth, δ, as well as magnetic anisotropy distribution within the metallic nucleus. Annealed and stress-annealed Co-rich microwires present rectangular hysteresis loop and single and fast domain wall propagation. However, Co-based stress-annealed microwires present high magnetoimpedance ratio. Observed stress-induced anisotropy and related changes of magnetic properties are discussed considering internal stresses relaxation and “back-stresses”.

Impact of Stress Annealing on the Magnetization Process of Amorphous and Nanocrystalline Co-Based Microwires.

The domain wall (DW) dynamics of amorphous and nanocrystalline Co-based glass-coated microwires are explored under the influence of stress annealing. Different annealing profiles have enabled remarkable changes in coercivity and magnetostriction values of Co-based amorphous microwires with initially negative magnitude, allowing induced magnetic bistability in stress-annealed samples and, consequently, high DW velocity has been observed. Similarly, Co-based nanocrystalline microwires with positive magnetostriction and spontaneous bistability have featured high DW velocity. Different values of tensile stresses applied during annealing have resulted in a redistribution of magnetoelastic anisotropy showing a decreasing trend in both DW velocities and coercivity of nanocrystalline samples. Observed results are discussed in terms of the stress dependence on magnetostriction and microstructural relaxation.

Effect of stress-induced anisotropy on high frequency magnetoimpedance effect of Fe and Co-rich glass-coated microwires

The influence of stress-annealing on the magnetic softness and the magnetoimpedance effect of Fe-and Co-based glass-coated microwires is studied. As-prepared Co-rich glass-coated microwires present better magnetic softness and rather higher magnetoimpedance ratio with a double-peak dependence, typical for materials with transverse magnetic anisotropy. As-prepared Fe-based microwires present a rectangular hysteresis loop with a coercivity an order of magnitude higher and a magnetoimpedance ratio of an order of magnitude lower. Stress-annealing of Co- and Fe-based glass-coated microwire allows considerable magnetoimpedance ratio increasing. The impact of stress-annealing is especially pronounced in a Fe-based microwire, where transverse magnetic anisotropy, large (an order of magnitude) improvement of the magnetic softness and magnetoimpedance ratio are observed.In Co-based microwire a magnetoimpedance ratio improvement for short annealing time and a change of hysteresis loop from linear to rectangular are observed. Observed stress-induced anisotropy and related changes of magnetic properties are discussed considering internal stresses relaxation and “back-stresses”.Obtained experimental results yield new and important insights into the influence of stress-induced magnetic anisotropy on the magnetoimpedance effect and hysteresis loops of glass-coated microwires.

Simultaneous Detection of Giant Magnetoimpedance and Fast Domain Wall Propagation in Co-Based Glass-Coated Microwires

The magnetic properties of as-prepared and annealed amorphous $\text{Co}_{{50}.{69}}{{\text {Fe}}_{{8}.{13}}}{{\text {Ni}}_{{17}.{55}}}{{\text {B}}_{{13}.{29}}}{{\text {Si}}_{{10}.{34}}}$ and glass-coated microwires produced by the Taylor–Ulitovsky technique are investigated systematically. Magnetic-field frequency dependences of magnetoimpedance (MI), domain-wall (DW) velocity, and hysteresis loops were measured. At certain annealing conditions, high MI and fast DW propagation simultaneously coexist. The results suggest criteria for the selection of materials for high-performance magnetic sensors.

Domain Wall Propagation in Co-Based Glass-Coated Microwires: Effect of Stress Annealing and Tensile Applied Stresses

RECENTLY, domain wall (DW) propagation in magnetic wires has been recognized as one of the important lines of research due to its potential use in magnetic devices [1]–[7]. The DW speed and the possibilities for the DW dynamics manipulation are quite relevant for these applications. Extremely fast DW propagation has been reported for amorphous magnetically bistable microwires with positive magnetostriction constant λs and circular cross section (usually, exceeding 1000 m/s) [3], [4]. On the other hand, ferromagnetic glass-coated microwires have attracted growing attention in the last few years, mostly owing to their outstanding soft magnetic properties (magnetic bistability, enhanced magnetic softness, Giant magnetoimpedance (GMI) effect, and fast DW propagation) [5]–[7]. These microwires have a composite character consisting of a cylindrical metallic nucleus of (1–30 μm) and glass coating (with thickness of 1–20 μm). These microwires can be prepared by the modified Taylor–Ulitvosky technique, which involves simultaneous rapid quenching and drawing of the metallic nucleus inside a glass capillary [6], [7]. Thus, strong stresses are introduced in the metallic nucleus arising from the drawing and quenching, as well as from the different thermal expansion coefficient between the glass sheath and the metallic nucleus [5], [6], [8]–[10]. Therefore, the magnetoelastic anisotropy induced by the internal stresses plays an important role in controlling their magnetic properties [4], [5], [7]–[9]. Fe-rich microwires with positive magnetostriction coefficient, λs , present magnetic bistability related to a large and single axially magnetized inner core. Therefore, one can observe quite fast magnetization switching within the single magnetic domain related with fast DW propagation. In particular, these materials are unique for studying the DW propagation since they can exhibit a very fast DW velocity [2]–[4], [6], [11]. On the other hand, it is well known that the DW dynamics in glasscoated microwires is strongly dependent to external parameters

Stress tunable microwave absorption of ferromagnetic microwires for sensing applications

In the present work, we have studied the low field absorption (LFA) at 9 GHz of a set of Co-based glass-coated microwires in the presence of tensile stresses along the wire axis. The results reveal that the absorption profiles bear valve-like features associated with microwave magnetoimpedance effect. The stress applied along the wire axis compensates the reverse effect of magnetic field on absorption. The peak shown in the derivative LFA spectra becomes wider with increasing stress and moves to higher field, corresponding to the magnetization process. A larger ratio of metal to total diameter was found to be favorable to microwave absorption due to the smaller anisotropy and also gave rise to a larger magnetostriction constant. The influences of stress/magnetic field on the absorption as well as the shift of feature stress with wire geometry were discussed in the context of an effective microwire-based sensor design. Calculations of magnetostriction constant by the derived field dependence of anisotropy field were also performed to demonstrate the usefulness of stress tunable microwave absorption characteristics as a research tool.