Glass-coated Microwires Research Articles

The Interplay of Core Diameter and Diameter Ratio on the Magnetic Properties of Bistable Glass-Coated Microwires

Glass-coated microwires exhibiting magnetic bistability have garnered significant attention as promising wireless sensing elements, primarily due to their rapid magnetization switching capabilities. These microwires consist of a metallic core with diameter d, encased in a glass coating, with a total diameter D. In this study, we investigated how the dimensions of both components and their ratio (d/D) influence the magnetization reversal behavior of Fe-based microwires. While previous studies have focused on either d or d/D individually, our research uniquely considered the combined effect of both parameters to provide a comprehensive understanding of their impact on magnetic properties. The metallic core diameter d varied from 10 to 19 µm and the d/D ratio was in the range of 0.48–0.68. To assess the magnetic properties of these microwires, including the shape of the hysteresis loop, coercivity, remanent magnetization, and the critical length of bistability, we employed vibrating sample magnetometry in conjunction with FORC-analysis. Additionally, to determine the critical length of bistability, magnetic measurements were conducted on microwires with various lengths, ranging from 1.5 cm down to 0.05 cm. Our findings reveal that coercivity is primarily dependent on the d/D parameter. These observations are effectively explained through an analysis that considers the competition between magnetostatic and magnetoelastic anisotropy energies. This comprehensive study paves the way for the tailored design of glass-coated microwires for diverse wireless sensing applications.

Anomalous magnetic behavior in MnFePSi glass-coated microwires

We studied the MnFePSi glass-coated microwires (GCMWS) prepared by using Taylor–Ulitovsky technique at low magnetic fields and low temperatures. While regular ferromagnetic behavior has been observed at room temperature, anomalous magnetic behavior is observed for the glass-coated microwires samples. Notable metamagnetic phase transition is observed for bulk alloy sample from the magnetic hysteresis loops measured at 5 K. Meanwhile, extraordinary metamagnetic phase transition is seen at hysteresis loops measured at temperature below 100 K. In addition, M-H loops show harder magnetic properties compared to the bulk sample, where the coercivity, Hc, of glass-coated microwire is about 64 times higher than the one reported in bulk alloy. Additionally, the hysteresis loops of glass-coated microwires measured at temperature lower than 100 K show multistep magnetic behaviour. Zero Field Cooling (ZFC), Field Cooling (FC) and Field Heating (FH) curves of bulk samples show totally different magnetic behaviour compared to the microwire sample measured at the same conditions due to the different microstructure phases for the bulk and microwires samples. The present findings demonstrate the significant impact of drawing, quenching and stresses induced by glass-coating on the microstructure and magnetic characteristics of MnFePSi-metallic alloys as compared to their bulk form. Furthermore, we confirmed that, in contrast to the bulk form constraint, the Taylor-Ulitovsky process for metallic glass-coating microwires may alter the physical characteristics and extend the applications of MnFePSi alloys.

Dependence of Magnetic Properties of As-Prepared Nanocrystalline Ni2MnGa Glass-Coated Microwires on the Geometrical Aspect Ratio.

We have prepared NiMnGa glass-coated microwires with different geometrical aspect ratios, ρ = dmetal/Dtotal (dmetal-diameter of metallic nucleus, and Dtotal-total diameter). The structure and magnetic properties are investigated in a wide range of temperatures and magnetic fields. The XRD analysis illustrates stable microstructure in the range of ρ from 0.25 to 0.60. The estimations of average grain size and crystalline phase content evidence a remarkable variation as the ρ-ratio sweeps from 0.25 to 0.60. Thus, the microwires with the lowest aspect ratio, i.e., ρ = 0.25, show the smallest average grain size and the highest crystalline phase content. This change in the microstructural properties correlates with dramatic changes in the magnetic properties. Hence, the sample with the lowest ρ-ratio exhibits an extremely high value of the coercivity, Hc, compared to the value for the sample with the largest ρ-ratio (2989 Oe and 10 Oe, respectively, i.e., almost 300 times higher). In addition, a similar trend is observed for the spontaneous exchange bias phenomena, with an exchange bias field, Hex, of 120 Oe for the sample with ρ = 0.25 compared to a Hex = 12.5 Oe for the sample with ρ = 0.60. However, the thermomagnetic curves (field-cooled-FC and field-heating-FH) show similar magnetic behavior for all the samples. Meanwhile, FC and FH curves measured at low magnetic fields show negative values for ρ = 0.25, whereas positive values are found for the other samples. The obtained results illustrate the substantial effect of the internal stresses on microstructure and magnetic properties, which leads to magnetic hardening of samples with low aspect ratio.

Bending annealing induced transformation of magnetic structure in Co-rich amorphous microwires

For the first time, the magnetic structure of a glass-coated microwire, previously subjected to bending annealing was investigated. Magnetic and magneto-optical analyses were performed after the sample was annealed and returned to a straightened state. Changes in the magnetic structure, induced by the bending annealing, were observed both within the microwire and on its surface. The spatial distribution of the magnetic structure was primarily attributed to the spatial distribution of the stress gradient resulting from bending stress. Special emphasis was placed on the transformation of surface domain structures, with the diversity of these structures indicating a significant influence of bending-annealing-unbending procedure on their formation process.

Tuning of magnetic bistability and domain wall dynamics in magnetic microwires

A unique combination of unusual magnetic properties, such as magnetic bistability associated with ultrafast domain wall propagation or ultrasoft magnetic properties, together with excellent mechanical and corrosion properties can be obtained in amorphous microwires. Such ferromagnetic microwires coated with insulating and flexible glass-coating with diameters ranging from 0.1 to 100 can be prepared using the Taylor-Ulitovsky method. Magnetic properties of glass-coated microwires are affected by chemical compositions of the metallic nucleus and can be substantially modified by post-processing. We provide an overview of the routes allowing tuning of hysteresis loops and domain wall dynamics in amorphous microwires and new experimental results on the dependence of hysteresis loops on external stimuli, such as applied stress and temperature.

Comparison of the Magnetic and Structural Properties of MnFePSi Microwires and MnFePSi Bulk Alloy.

We provide comparative studies of the structural, morphological, microstructural, and magnetic properties of MnFePSi-glass-coated microwires (MnFePSi-GCMWs) and bulk MnFePSi at different temperatures and magnetic fields. The structure of MnFePSi GCMWs prepared by the Taylor-Ulitovsky method consists of the main Fe2P phase and secondary impurities phases of Mn5Si3 and Fe3Si, as confirmed by XRD analysis. Additionally, a notable reduction in the average grain size from 24 µm for the bulk sample to 36 nm for the glass-coated microwire sample is observed. The analysis of magnetic properties of MnFePSi-glass-coated microwires shows different magnetic behavior as compared to the bulk MnFePSi. High coercivity (450 Oe) and remanence (0.32) are observed for MnFePSi-GCMWs compared to low coercivity and remanent magnetization observed for bulk MnFePSi alloy. In addition, large irreversibility at low temperatures is observed in the thermal dependence of magnetization of microwires. Meanwhile, the bulk sample shows regular ferromagnetic behavior, where the field cooling and field heating magnetic curves show a monotonic increase by decreasing the temperature. The notable separation between field cooling and field heating curves of MnFePSi-GCMWs is seen for the applied field at 1 kOe. Also, the M/M5K vs. T for MNFePSi-GCMWs shows a notable sensitivity at a low magnetic field compared to a very noisy magnetic signal for bulk alloy. The common features for both MnFePSi samples are high Curie temperatures above 400 K. From the experimental results, we can deduce the substantial effect of drawing and quenching involved in the preparation of glass-coated MnFePSi microwires in modification of the microstructure and magnetic properties as compared to the same bulk alloy. The provided studies prove the suitability of the Taylor-Ulitovsky method for the preparation of MnFePSi-glass-coated microwires.

Exploring the temperature dependence of magnetic properties and magnetoimpedance effect in Co-rich microwires

We studied the temperature dependence of the magnetic properties and giant magnetoimpedance, GMI, effect in as-prepared and annealed Co69.2Fe3.6Ni1B12.5Si11Mo1.5C1.2 glass-coated microwires with nearly-zero magnetostriction. Substantial changes in the GMI ratio, ΔZ/Z, value and magnetic field, H, dependence, and in the hysteresis loops upon heating were observed. The modification in the hysteresis loop shape upon heating correlates with a change in the ΔZ/Z (H) dependencies. In as-prepared and most of the heat treated samples the hysteresis loop transformation from inclined to squared upon heating correlates with the change in ΔZ/Z(H) dependencies from double-peak to single-peak. However, the stress-annealed at 118 MPa samples present better thermal stability of the ΔZ/Z(H) dependencies and hysteresis loops. In all the studied samples an increase in the GMI ratio at 300 °C was observed. The origin of the observed temperature dependences is discussed in terms of the Hopkinson effect, temperature dependence and relaxation of internal stresses, induced magnetic anisotropy, and temperature dependence of the magnetostriction coefficient.

Contactless in-vivo temperature sensing in spinal cord based on magnetically bistable microwire

We have employed a magnetically bistable glass coated microwire as a passive contactless sensing element for in-vivo temperature monitoring in the rat’s spinal cord. The single piece (1 cm long) of Fe76Cr2Mo6B15Cu1 microwire was epidurally implanted into the adult female Wistar rats. The magnetization switching was measured in-vivo within the temperature range of 34.5–41.0 °C. Results show a monotonous temperature decrease of the switching time whose fitting to a second order polynomial dependence allows one to conclude a sensitivity down to 0.01ºC within the measured interval. Biocompatibility study shows that cells have a high affinity to the glass-coated microwire, and their viability is not influenced by the experimental condition under which the microwire’s response is measured. Finally, a histology study reveals that no histopathological changes or tissue reactions were observed even after 9 months of implantation.

Preparation and magnetic properties of MnFePSi-based glass-coated microwires

We prepared a Mn48Fe22P15Si15 glass-coated microwires (GCMWS) with metallic nucleus diameter, d = 11.2 μm and total diameter, D = 28.3 μm (geometrical aspect ratio d/D = 0.4) for the first time by using the Taylor–Ulitovsky Technique. This low-cost, single-step fabrication approach enabled the preparation of kilometers-long GCMWS from a few grams of low-cost components (Mn, Fe, P, and Si) for a variety of applications. The analysis of the magnetic measurements revealed a well-defined magnetic anisotropy in the whole temperature range. Moreover, relatively hard magnetic properties were observed for the temperature range of 5–400 K, where the average of coercivity, Hc ≈ 465 Oe. Notable magnetic field, H, and temperature dependencies of the magnetic properties were observed. Substantially irreversible magnetic behavior with a blocking temperatures Tb = 97 K at H = 1 kOe and Tb = 50 K at H = 5 kOe upon field cooling was observed. The modification in the magnetic properties of MnFePSi-glass-coated microwires is ascribed to the presence of various magnetic phases resulting from internal stresses induced by the glass coating. Moreover, the elevated Curie temperature (Tc > 400 K) observed in the investigated sample, makes this material as an appealing choice for several industrial applications.

RTD fluxgate sensors based on current induced magnetization reversal in twisted glass-coated microwires

RTD fluxgate sensors based on current induced magnetization reversal in twisted glass-coated microwires

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

Magnetic Properties and Applications of Glass-coated Ferromagnetic Microwires

A remarkable magnetic softness and giant magnetoimpedance (GMI) effect at GHz frequency range havebeen observed in glass-coated microwires subjected to appropriate postprocessing. Co-based microwires present higher GMI effect. Insulating and flexible glass-coating allows use of magnetically soft amorphous glass-coated microwires for stresses or temperature monitoring insmartcomposites using free space facility. Such composites with magnetic microwire inclusions can present tunable magnetic permittivity. We report on in-situ the evolution of the transmission and reflection parameters of the polymer containing magnetic microwire inclusions during the polymerization process. A remarkable change of the reflection and transmission in the range of 4-7 GHz upon the matrix polymerization is observed. Observed dependencies are discussed in terms of the effect of the temperature and stresses variation on magnetic properties of glass-coated microwires during the thermoset matrix polymerization. Obtained results are considered as a base for novel sensing technique allowing non-destructive and non-contact monitoring of the composites utilizing ferromagnetic glass-coated microwire inclusions with magnetic properties sensitive to tensile stress and temperature.

Magnetic Properties of Co2MnSi-Based Heusler Alloy Glass-Coated Microwires

Magnetic Properties of Co₂MnSi-Based Heusler Alloy Glass-Coated Microwires

Unveiling the Magnetic and Structural Properties of (X2YZ; X = Co and Ni, Y = Fe and Mn, and Z = Si) Full-Heusler Alloy Microwires with Fixed Geometrical Parameters

We studied Ni2FeSi-, Co2FeSi-, and Co2MnSi-based full-Heusler alloy glass-coated microwires with the same geometric parameters, i.e., fixed nucleus and total diameters, prepared using the Taylor–Ulitovsky method. The fabrication of X2YZ (X = Co and Ni, Y = Fe and Mn, and Z = Si)-based glass-coated microwires with fixed geometric parameters is quite challenging due to the different sample preparation conditions. The XRD analysis showed a nanocrystalline microstructure for all the samples. The space groups Fm3¯m (FCC) and Im3¯m (BCC) with disordered B2 and A2 types are observed for Ni2FeSi and Co2FeSi, respectively. Meanwhile, a well-defined, ordered L21 type was observed for Co2MnSi GCMWs. The change in the positions of Ni, Co and Mn, Fe in X2YSi resulted in a variation in the lattice cell parameters and average grain size of the sample. The room-temperature magnetic behavior showed a dramatic change depending on the chemical composition, where Ni2FeSi MWs showed the highest coercivity (Hc) compared to Co2FeSi and Co2MnSi MWs. The Hc value of Ni2FeSi MWs was 16 times higher than that of Co2MnSi MWs and 3 times higher than that of Co2FeSi MWs. Meanwhile, the highest reduced remanence was reported for Co2FeSi MWs (Mr = 0.92), being about 0.82 and 0.22 for Ni2FeSi and Co2MnSi MWs, respectively. From the analysis of the temperature dependence of the magnetic properties (Hc and Mr) of X2YZ MWs, we deduced that the Hc showed a stable tendency for Co2MnSi and Co2FeSi MWs. Meanwhile, two flipped points were observed for Ni2FeSi MWs, where the behavior of Hc changed with temperature. For Mr, a monotonic increase on decreasing the temperature was observed for Co2FeSi and Ni2FeSi MWs, and it remained roughly stable for Co2MnSi MWs. The thermomagnetic curves at low magnetic field showed irreversible magnetic behavior for Co2MnSi and Co2FeSi MWs and regular ferromagnetic behavior for Ni2FeSi MWs. The current result illustrates the ability to tailor the structure and magnetic behavior of X2YZ MWs at fixed geometric parameters. Additionally, a different behavior was revealed in X2YZ MWs depending on the degree of ordering and element distribution. The tunability of the magnetic properties of X2YZ MWs makes them suitable for sensing applications.

The Magnetostriction of Amorphous Magnetic Microwires: The Role of the Local Atomic Environment and Internal Stresses Relaxation

We studied the magnetostriction coefficients, λs, Curie temperature, Tc, and their dependence on annealing conditions in Fe47Ni27Si11B13C2 and Co67Fe3.9Ni1.5B11.5Si14.5Mo1.6 amorphous glass-coated microwires with rather different character of hysteresis loops. A positive λs ≈ 20 × 10−6 is observed in as-prepared Fe47Ni27Si11B13C2, while low and negative λs ≈ −0.3 × 10−6 is obtained for Co67Fe3.9Ni1.5B11.5Si14.5Mo1.6 microwire. Annealing affects the magnetostriction coefficients and Curie temperatures, Tc, of both Fe47Ni27Si11B13C2 and Co67Fe3.9Ni1.5B11.5Si14.5Mo1.6 glass-coated microwires in a similar way. Observed dependencies of hysteresis loops, λs and Tc on annealing conditions are discussed in terms of superposition of internal stresses relaxation and structural relaxation of studied microwires. We observed linear λs dependence on applied stress, σ, in both studied microwires. A decrease in the magnetostriction coefficient upon applied stress is observed for Co-rich microwires with low and negative magnetostriction coefficient. On the contrary, for Fe-Ni-rich microwires with a positive magnetostriction coefficient, an increase in the magnetostriction coefficient with applied stress is observed. The observed results are discussed considering the internal stresses relaxation and short range atomic rearrangements induced by annealing on hysteresis loops, magnetostriction coefficients and Curie temperatures of studied microwires.

Effect of shell-induced stresses on the magnetic properties of Fe-based glass-coated microwires: Accounting of initial technical parameters

The study focuses on examining the impact of shell-induced stresses on the magnetic characteristics of Fe-based microwires encased in glass, with particular attention given to the critical fabrication parameters employed in the microwire production process utilizing the Taylor-Ulitovsky method. We systematically investigate how internal stresses affect magnetization reversal behaviors in both glass-coated and uncoated Fe77.5Si7.5B15 microwires through experimental analysis and compare these effects with those resulting from stress-annealing procedures. The simulation of stress distribution caused by the solidification process is based on thermo viscoelasticity theory considering a non-constant glass transition temperature. The analysis also includes the knowledge of the initial parameters of the microwires during the manufacturing.

Influence of the Geometrical Aspect Ratio on the Magneto-Structural Properties of Co2MnSi Microwires

This present study illustrates the strong effect of geometrical parameters on the magneto-structural properties of Co2MnSi glass-coated microwires prepared using the Taylor–Ulitovsky method. Thus, there are three samples with different geometrical aspect ratios (ρ). The XRD analysis shows a significant change by modifying the aspect ratio; for ρ = 0.42, the main peak with miller indices (220) is recognized as an A2-type disordered cubic structure. For the sample with ρ = 0.46, mixed L21 and B2 cubic structures are observed. Meanwhile, in the sample with a low aspect ratio, ρ = 0.30, the perfect L21 ordered cubic structure is attained. Magnetic characterization has been carried out at a wide range of temperatures and magnetic fields. A significant increase in coercivity and normalized reduced remanence by decreasing the aspect ratio is detected. The change in the magnetic properties is attributed to the modification in the microstructure, which is induced during the fabrication process. Such a dependence on the microstructure and magnetic properties on the ρ-ratio can be associated either with the internal stress distribution and magnitude or with different quenching rates of microwires with different aspect ratios. The current findings demonstrate the tunability of the microstructure and magnetic properties of Co2MnSi-glass-coated microwires simply via a small modification in the geometric properties during the manufacturing process and without excreting any additional post-processing. The variation in the geometric parameters of Co2MnSi glass-coated microwires allows us to tune the magnetic properties and structure, which is essentially advantageous for sensing device development.

Anomalous Magnetic Anisotropy Behaviour in Co-Rich and Fe-Rich Glass-Coated Microwires under Applied Stress.

In this article, we study the effect of annealing temperature and applied stress on the magnetic properties of Fe71.80B13.27Si11.02Nb2.99Ni0.92 and Co65.34Si12.00B10.20Cr8.48Fe3.90Mo0.08 microwires. An anomalous behavior of the coercive field is observed while applying stress, indicating nontrivial changes in the microwire magnetic anisotropy. The effect of applied stimuli on the magnetic anisotropy and magnetostriction constant in both microwires is also discussed.

Optimization of Magnetoimpedance Effect and Magnetic Properties of Fe-Rich Glass-Coated Microwires by Annealing.

As-prepared Fe-rich microwires with perfectly rectangular hysteresis loops present magnetization reversal through fast domain wall propagation, while the giant magnetoimpedance (GMI) effect in Fe-rich microwires is rather low. However, the lower cost of Fe-rich microwires makes them attractive for magnetic sensors applications. We studied the effect of conventional (furnace) annealing and Joule heating on magnetic-propertied domain wall (DW) dynamics and the GMI effect in two Fe microwires with different geometries. We observed that magnetic softness, GMI effect and domain wall (DW) dynamics can be substantially improved by appropriate annealing. Observed experimental results are discussed considering the counterbalance between the internal stresses relaxation and induced magnetic anisotropy associated with the presence of an Oersted magnetic field during Joule heating.

Carbon-Doped Co2MnSi Heusler Alloy Microwires with Improved Thermal Characteristics of Magnetization for Multifunctional Applications.

In the current work, we illustrate the effect of adding a small amount of carbon to very common Co2MnSi Heusler alloy-based glass-coated microwires. A significant change in the magnetic and structure structural properties was observed for the new alloy Co2MnSiC compared to the Co2MnSi alloy. Magneto-structural investigations were performed to clarify the main physical parameters, i.e., structural and magnetic parameters, at a wide range of measuring temperatures. The XRD analysis illustrated the well-defined crystalline structure with average grain size (Dg = 29.16 nm) and a uniform cubic structure with A2 type compared to the mixed L21 and B2 cubic structures for Co2MnSi-based glass-coated microwires. The magnetic behavior was investigated at a temperature range of 5 to 300 K and under an applied external magnetic field (50 Oe to 20 kOe). The thermomagnetic behavior of Co2MnSiC glass-coated microwires shows a perfectly stable behavior for a temperature range from 300 K to 5 K. By studying the field cooling (FC) and field heating (FH) magnetization curves at a wide range of applied external magnetic fields, we detected a critical magnetic field (H = 1 kOe) where FC and FH curves have a stable magnetic behavior for the Co2MnSiC sample; such stability was not found in the Co2MnSi sample. We proposed a phenomenal expression to estimate the magnetization thermal stability, ΔM (%), of FC and FH magnetization curves, and the maximum value was detected at the critical magnetic field where ΔM (%) ≈ 98%. The promising magnetic stability of Co2MnSiC glass-coated microwires with temperature is due to the changing of the microstructure induced by the addition of carbon, as the A2-type structure shows a unique stability in response to variation in the temperature and the external magnetic field. In addition, a unique internal mechanical stress was induced during the fabrication process and played a role in controlling magnetic behavior with the temperature and external magnetic field. The obtained results make Co2MnSiC a promising candidate for magnetic sensing devices based on Heusler glass-coated microwires.