Co-rich Glass-coated Microwires Research Articles

Effect of temperature on magnetic properties and magnetoimpedance effect of Co-rich glass-coated microwires

Effect of temperature on magnetic properties and magnetoimpedance effect of Co-rich glass-coated microwires

Stress-Induced Magnetic Anisotropy Enabling Engineering of Magnetic Softness and GMI Effect of Amorphous Microwires

Stress-annealing enabled a considerable improvement in the GMI effect in both Fe- and Co-rich glass-coated microwires. Additionally, a remarkable magnetic softening can be achieved in stress-annealed Fe-rich microwires. Observed stress-annealing induced magnetic anisotropy is affected by annealing conditions (temperatures and stresses applied during annealing). The highest GMI ratio up to 310% was obtained in stress-annealed Co-rich microwires, although they presented rectangular hysteresis loops. A remarkable magnetic softness and improved GMI ratio over a wide frequency range were obtained in stress-annealed Fe-rich microwires. Irregular magnetic field dependence observed for some stress-annealing conditions is attributed to the contribution of both the inner axially magnetized core and outer shell, with transverse magnetic anisotropy.

Stress dependence of the magnetic properties of glass-coated amorphous microwires

We studied the effect of applied tensile stresses on magnetic properties of Fe- and Co-rich amorphous glass-coated microwires. Rising of magnetic anisotropy field upon tensile stress in Co-rich glass-coated microwires is described by a linear dependence. Furthermore, decrease of magnetic susceptibility upon tensile stress is observed in Co-rich microwires. A monotonous increase in the coercivity and the switching field upon tensile applied stress is observed for as-prepared Fe-rich microwire. Stress induced magnetic bistability consisting of transformation of hysteresis and onset of rectangular hysteresis loop upon tensile stress, σ, of about 22.5 MPa is observed in stress-annealed Fe-rich microwires. Such stress-induced magnetic bistability results in considerable growing of coercivity and remanent magnetization in stress-annealed Fe-rich microwires. The rising in the coercivity and the switching field upon applied tensile stresses in stress-annealed Fe-rich microwires with stress induced magnetic bistability (at σ > 22.5 MPa) is roughly described by the σ½ dependence, as previously reported for the wires with spontaneous magnetic bistability. Consequently, stress-annealing of Fe-rich microwire allows beneficial enhancement of the stress dependence of coercivity. Observed dependencies are discussed considering stress dependence of the magnetostriction coefficient in Co-rich glass-coated microwires, internal stresses redistribution and domain structure rearrangement in stress-annealed Fe-rich microwires upon applied tensile stresses.

Magnetic anisotropy and stress-magnetoimpedance (S-MI) in current-annealed Co-rich glass-coated microwires with positive magnetostriction

Abstract Effects of a dc current annealing, in terms of magnitude and inflow time, on magnetic hysteresis properties, magnetoimpedance (MI) and stress-magnetoimpedance (S-MI) in glass-coated amorphous Co71Fe5B11Si10Cr3 microwires with a small positive magnetostriction were investigated in this work. The annealing process combining Joule-heating and circular magnetic field leads to the creation of a specific magnetic anisotropy of a helical or circular type, and consequently, is helpful to control the MI and S-MI behaviours making them more suitable for particular sensing applications. After annealing, the magnetoimpedance plots transformed from a bell-shaped typical of an axial easy anisotropy to the shape with two symmetrical peaks, the magnitude and position of which are controlled with the annealing current parameters. Applying a tensile stress on the annealed wires changes the easy anisotropy direction which leads to the potential for highly sensitive S-MI without use of dc bias fields. A stress sensitivity of more than 260% at σ ex = 250 MPa at zero magnetic field is achieved.

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.

Investigation of the properties of Co-rich amorphous ferromagnetic microwires by means of small angle magnetization rotation method

The amplitude of the second harmonic of the electro-motive force occurring in the receiving pick-up coil when alternating electrical current is flowing through the microwire is measured as a function of applied external magnetic field, at different mechanical tensile stresses. In addition, an analytical expression for the amplitude of the second harmonic of the electro-motive force is derived. Comparing the experimental and theoretical data the saturation magnetization, the magnetostriction constant and the amplitude of the residual quenching stress have been determined for a family of Co-rich glass-coated microwires.

High-frequency GMI effect in glass-coated amorphous wires

The giant magneto-impedance (GMI) attracted growing attention especially owing to the large sensitivity of the electrical impedance to the DC magnetic field, when the relatively high-frequency electrical current flows along the magnetic conductor. Such GMI effect is the highest in soft magnetic wires with vanishing magnetostriction constant. The last strong tendency in miniaturization of the magnetic sensing elements has resulted in the development of the thinner glass-coated wires produced by the Taylor–Ulitovsky method (1–30 μm in diameter). Recent significant progress in tailoring of magnetically soft Co-rich glass-coated microwires allows to enhance significantly the GMI ratio (up to about 600%) in compositions with vanishing magnetostriction constant, λ s, at frequencies between 100 kHz and 20 MHz. In this paper we report novel results on the GMI effect at high-frequency region (between 10 MHz and 500 MHz) in different families of amorphous microwires (Fe-rich, with positive magnetostriction constant, Co-rich with negative magnetostriction constant and Co–Fe-rich with nearly-zero magnetostriction constant) fabricated by the Taylor–Ulitovsky method. The differences in observed dependencies for these families of compositions have been interpreted in terms of difference in the magnetoelastic anisotropy.