Glass-coated Microwires Research Articles

Anomalous magnetic behavior in half-metallic Heusler Co2FeSi alloy glass-coated microwires with high Curie temperature

In the current study, we have succeeded to fabricate Co2FeSi Heusler alloy glass-covered microwires with magnetic core nucleus diameter d = 4.36 µm and total diameter D = 17.55 µm, with high Curie temperature (Tc>1100 K) and well-defined magnetic anisotropy for high temperature spintronic devices application. The magnetic properties of as-prepared and annealed at different temperature (873 K, 973 K and 1073 K for 1 h) of Co2FeSi Heusler alloy glass-covered microwires have been investigated. Strong dependence of the magnetic properties on the annealing conditions has been indicated. Anomalous magnetic behavior for annealed samples at 873 K and 973 K has been found and structural properties of such samples have been analyzed. Critical temperatures 155 K and 250 K have been detected for annealed samples at 873 K and 973 K, respectively, where the behavior of M-H loops and coercivity changed. Below the critical point the M-H curve shows “kink or wasp-waisted” magnetic behavior and complex magnetic reversal mechanism is supposed. The anomalous magnetic behavior is due to the martensitic phases induced by annealing conditions below the room temperature. This unusual magnetization behavior provides opportunities to understand the phenomena of different types of magnetic domain structures in the preferred crystallographically oriented Co2FeSi Heusler alloy glass-coated micro-wires, essentially helpful for designing the devices based on magnetization switching.

Non-Destructive Testing of Pipe Conveyor Belts Using Glass-Coated Magnetic Microwires

Belt conveyors have been used in a wide range of applications because in comparison to the alternative solutions represented by the rail or road transportation, their operation is typically more cost effective, with lower energy demands and the possibility of utilizing renewable energy sources, and during their operation, less noise and air pollution is produced. The presented article is focused on pipe belt conveyors that are even more sustainable and in harmony with the environment, especially considering transportation of fine and dusty materials. More specifically, pipe belt conveyors have the possibility of utilizing microwires as a sensing element for microwire-based sensors for the pipe belt conveyor diagnostics from a mechanical loading point of view. This is because during the enclosing of the pipe conveyor belt, periodical cyclical mechanical loading is applied due to the bending. From the results of the performed set of FEM (Finite Element Method) analyses of the glass-coated magnetic microwires, it can be concluded that during the selection process of the microwires, emphasis should be directed the thickness of the glass coating, which can affect the lifetime of the microwire significantly. The microwire length has negligible influence on the estimated number of bending cycles until the damage or crack occurs.

Analysis of magnetocaloric effect in Ni2FeGa-based glass-coated microwires

Enhancement of magnetocaloric effect by proper tuning of phase transition temperatures was analysed on a series of Ni2FeGa Heusler glass-coated microwires. By a targeted combination of the structural and magnetic transition, the magnetic entropy change was enhanced more than three times from ≈ −0.25 J.kg−1.K−1 at 125 K to ≈ −0.8 J.kg−1.K−1 at the human body temperature 310 K, and cooling power increased significantly. In the presented investigation, different analytical approaches like the temperature-dependent magnetisation, magnetic entropy change, Arrott plots, universal curves analysis, n-exponent and Kouvel-Fisher method were performed to verify the presence and contribution of both types of transitions. The results show the possibility of establishing a phase diagram with the correlation between the structural and magnetic transition temperature as a function of the valence electrons concentration ratio (e/a) – chemical composition. Moreover, obtained results point to the fact that the transition temperatures are invariant under different analytical approaches. The phase diagram allows fine-tuning of the magnetocaloric effect in Ni2FeGa-based Heusler alloys in the form of glass-coated microwires and opens the opportunity to achieve higher efficiency of magnetocaloric effect by a slight change of alloy’s composition.

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

In this work, we were able to produce Co2FeSi Heusler alloy glass-covered microwires with a metallic nucleus diameter of about 4.4 µm and total sample diameter of about 17.6 μm by the Taylor–Ulitovsky Technique. This low cost and single step fabrication process allowed the preparation of up to kilometers long glass-coated microwires starting from a few grams of high purity inexpensive elements (Co, Fe and Si), for a wide range of applications. From the X-ray diffraction, XRD, analysis of the metallic nucleus, it was shown that the structure consists of a mixture of crystalline and amorphous phases. The single and wide crystalline peak was attributed to a L21 crystalline structure (5.640 Å), with a possible B2 disorder. In addition, nanocrystalline structure with an average grain size, Dg = 17.8 nm, and crystalline phase content of about 52% was obtained. The magnetic measurements indicated a well-defined magnetic anisotropy for all ranges of temperature. Moreover, soft magnetic behavior was observed for the temperature measuring range of 5–1000 K. Strong dependence of the magnetic properties on the applied magnetic field and temperature was observed. Zero field cooling and field cooling magnetization curves showed large irreversibility magnetic behavior with a blocking temperature (TB = 205 K). The in-plane magnetization remanence and coercivity showed quite different behavior with temperature, due to the existence of different magnetic phases induced from the internal stress created by the glass-coated layer. Moreover, a high Curie temperature was reported (Tc ≈ 1059 K), which predisposes this material to being a suitable candidate for high temperature spintronic applications.

Effect of Joule heating on GMI and magnetic properties of Fe-rich glass-coated microwires

Influence of Joule heating on magnetic properties and GMI effect of Fe75B9Si12C4 glass-coated microwires was studied. A decrease in coercivity after Joule heating is observed, while hysteresis loops of Joule heated samples maintain a rectangular shape. However, a remarkable increase in GMI ratio is observed in Joule heated samples. Observed GMI ratio improvement has been discussed considering magnetic anisotropy induced by Oersted magnetic field during Joule heating and internal stress relaxation. A remarkable GMI effect improvement observed in Joule heated Fe-rich microwires, along the fact that Fe is a more common, less expensive metal than Co, makes them suitable for magnetic sensor applications.

Graded magnetic anisotropy in Co-rich microwires

A gradual change in the hysteresis loop of Co-rich glass-coated microwire sample stress-annealed at variable temperature is observed. Such microwire annealed with a temperature gradient presents also variable squareness ratio along the microwire length, L. Obtained graded anisotropy has been attributed to a gradual modification of the domain structure along the microwire. Accordingly, we propose a rather simple route to design graded magnetic anisotropy in a magnetic microwire.

Direct Visualization of a Domain Wall Pinning by Time-Resolved Microscopy in Amorphous Glass-Coated Microwires

Amorphous glass-coated microwires with positive magnetostriction are composite material with very fast domain wall (DW) propagation that can reach up to 18 km/s. Previously it was shown that such high DW velocity can be explained by the tilted orientation of a DW in static or quasi-static experimental conditions. Here we perform time-resolved observation of a DW in propagation. The shape of a DW is studied via magneto-optical Kerr effect (MOKE) imaging. Time-resolved MOKE microscope operating in the single-shot regime and a static mode is used to ascertain the role of surface pinning on DW velocity fluctuation. It is shown that a tilted DW undergoes complex DW distortions on a local scale.

Tuning of Magnetoimpedance Effect and Magnetic Properties of Fe-Rich Glass-Coated Microwires by Joule Heating.

The influence of Joule heating on magnetic properties, giant magnetoimpedance (GMI) effect and domain wall (DW) dynamics of Fe75B9Si12C4 glass-coated microwires was studied. A remarkable (up to an order of magnitude) increase in GMI ratio is observed in Joule heated samples in the frequency range from 10 MHz to 1 GHz. In particular, an increase in GMI ratio, from 10% up to 140% at 200 MHz is observed in Joule heated samples. Hysteresis loops of annealed samples maintain a rectangular shape, while a slight decrease in coercivity from 93 A/m to 77 A/m, after treatment, is observed. On the other hand, a modification of MOKE hysteresis loops is observed upon Joule heating. Additionally, an improvement in DW dynamics after Joule heating is documented, achieving DW propagation velocities of up to 700 m/s. GMI ratio improvement along with the change in MOKE loops and DW dynamics improvement have been discussed considering magnetic anisotropy induced by Oersted magnetic fields in the surface layer during Joule heating and internal stress relaxation. A substantial GMI ratio improvement observed in Fe-rich Joule-heated microwires with a rectangular hysteresis loop and fast DW propagation, together with the fact that Fe is a more common and less expensive metal than Co, make them suitable for use in magnetic sensors.

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”.

Vol4 num4-17 Smart composites with magnetic microwire inclusions allowing non-contact stress and temperature monitoring

We observed evolution of the transmission and reflection parameters of the composites contaning magnetic microwire inclusions during the composites matrix polymerization. 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 considering variation of temperature and stresses during the thermoset matrix polymerization and their influence on magnetic properties of glass-coated microwires. 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.

Ultralight Broadband Microwave Absorbing Materials Basing on Short Fibers of the Glass-Coated Amorphous Magnetic Microwires

Ultralight Broadband Microwave Absorbing Materials Basing on Short Fibers of the Glass-Coated Amorphous Magnetic Microwires

Ultralight Broadband Microwave-Absorbing Materials Based on the Short Fibers of Glass-Coated Amorphous Magnetic Microwires

Ultralight Broadband Microwave-Absorbing Materials Based on the Short Fibers of Glass-Coated Amorphous Magnetic Microwires

Ultralight Broadband Microwave Absorbing Materials Basing on Short Fibers of the Glass-Coated Amorphous Magnetic Microwires

Ultralight Broadband Microwave Absorbing Materials Basing on Short Fibers of the Glass-Coated Amorphous Magnetic Microwires

Anomalous Magnetic Behavior in Half-Metallic Heusler Co2fesi Alloy Glass-Coated Microwires with High Curie Temperature

Anomalous Magnetic Behavior in Half-Metallic Heusler Co2fesi Alloy Glass-Coated Microwires with High Curie Temperature

Analysis of Magnetocaloric Effect in Ni2fega-Based Glass-Coated Microwires

Analysis of Magnetocaloric Effect in Ni2fega-Based Glass-Coated Microwires

Manipulation of Magnetic and Structure Properties of Ni2fesi Glass-Coated Microwires by Annealing

Manipulation of Magnetic and Structure Properties of Ni2fesi Glass-Coated Microwires by Annealing

Analysis of Magnetocaloric Effect in Ni2fega-Based Glass-Coated Microwires

Analysis of Magnetocaloric Effect in Ni2fega-Based Glass-Coated Microwires

Development of Co-Rich Microwires with Graded Magnetic Anisotropy.

In this paper, a gradual change in the hysteresis loop of Co-rich glass-coated microwire stress-annealed at variable temperature is observed. Such microwires annealed with a temperature gradient also present a variable squareness ratio and magnetic anisotropy field along the microwire’s length. The obtained graded anisotropy has been attributed to a gradual modification of the domain structure along the microwire originated by a counterbalance between shape, magnetoelastic, and induced magnetic anisotropies. Accordingly, we propose a rather simple route to design graded magnetic anisotropy in a magnetic microwire.

Fe–Mn–Ga shape memory glass-coated microwire with sensing possibilities

The structural phase transformation in a non-stoichiometric shape memory Fe42.8Mn27.6Ga29.6 Heusler glass-coated microwire was experimentally observed using indirect magnetic, permeability, and electrical resistance measurements. While the temperature dependence of magnetization revealed hysteresis of magnetization during the heating and cooling process, magnetic hysteresis loops point to the change in the direction of the easy magnetization axis of the low- and high-temperature phase. Additionally, the unusual behavior of the permeability and electrical resistance measurements are in good agreement with the magnetic measurements. The x-ray diffraction profile measured at room temperature revealed the coexistence of a high-temperature L21 phase (a= 5.88 Å) and low-temperature phase with the L12 structure (a = 3.71 Å) and can be considered as another proof of the shape memory effect that is expected in the Fe–Mn–Ga-based Heusler alloys. In the presented glass-coated microwire, it is not only possible to shift the transformation temperature with the external magnetic field, but from its initial permeability value, it is possible to determine whether the alloy has undergone the structural transformation. Therefore, the presented Fe–Mn–Ga-based glass-coated microwire may be considered a suitable candidate for microactuators with sensory capabilities.

Pre-use interfacial shear strength prediction for fiber-reinforced thermosetting composites based on stress-impedance effect of ferromagnetic microwires

A new rapid evaluation method of composite interfacial shear strength (IFSS) on basis of impedance parameter utilizing the glass-coated cobalt-based ferromagnetic microwire (GCM) with sensitive stress-impedance effect is proposed. The intrinsic properties analysis and surface modification of GCM were performed to improve the sensitivity of stress-impedance effect and meet the application requirements in composites. The correlation between impedance increments and interfacial stress is investigated for GCM composites with different resin embedded lengths through experimental verification and finite element simulation. The impedance increment of microwire shows a high degree of dependence on IFSS of GCM/resin systems, which is mainly associated with the local interfacial stress from the resin. Based on this correlation mechanism and IFSS measured by microdroplet debonding test, IFSS of composites with different resin matrix were successfully calculated from the impedance parameter, and the interfacial bonding of resin matrix could be distinguished and sorted as relatively superior or inferior conveniently and rapidly. In comparison with the sophisticated, lengthy and expensive interface mechanical tests after the manufacture of fibers and resin, the pre-use efficient interfacial assessing of resin matrixes only using GCM shows potential to screen resin matrix with excellent interfacial properties towards advanced fiber-reinforced thermosetting resin matrix composite.