Search Results (33)

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/M_5K 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. Full article

Magnetic microwires with amorphous structures can present a unique combination of excellent magnetic softness and giant magnetoimpedance (GMI) effects together with reduced dimensions and good mechanical properties. Such unique properties make them suitable for various technological applications. The high GMI effect, observed in as-prepared Co-rich microwires, can be further optimized by postprocessing. However, unexpected magnetic hardening and a transformation of the linear hysteresis loop into a rectangular loop with a coercivity on the order of 90 A/m were observed in several Co-rich microwires upon conventional annealing. Several routes to improve magnetic softness and GMI effect in Fe- and Co-rich magnetic microwires are provided. We observed that stress annealing could remarkably improve the magnetic softness and GMI ratio of Co-rich microwires. Thus, almost unhysteretic loops with a coercivity of 2 A/m and a magnetic anisotropy field of about 70 A/m are achieved in Co-rich microwires stress annealed at appropriate conditions. The observed change in hysteresis loops and the GMI effect is explained by stress-annealing-induced anisotropy, which is affected by the stresses applied during annealing and by the annealing temperature. While as-prepared Fe-rich amorphous microwires present a low GMI effect, appropriate postprocessing (annealing and stress annealing) allows for a remarkable GMI ratio improvement (an order of magnitude). The evaluated dependence of the maximum GMI ratio on frequency allows the identification of the optimal frequency band for the studied samples. The origin of stress-annealing-induced anisotropy and related changes in hysteresis loops and the GMI effect are discussed in terms of the relaxation of internal stresses, “back-stresses”, as well as structural anisotropy. Full article

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 (H_c) compared to Co₂FeSi and Co₂MnSi MWs. The H_c 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 (H_c and M_r) of X₂YZ MWs, we deduced that the H_c showed a stable tendency for Co₂MnSi and Co₂FeSi MWs. Meanwhile, two flipped points were observed for Ni₂FeSi MWs, where the behavior of H_c changed with temperature. For M_r, 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. Full article

We studied the magnetostriction coefficients, λ_s, Curie temperature, T_c, and their dependence on annealing conditions in Fe₄₇Ni₂₇Si₁₁B₁₃C₂ and Co₆₇Fe_3.9Ni₁.₅B₁₁.₅Si_14.5Mo_1.6 amorphous glass-coated microwires with rather different character of hysteresis loops. A positive λ_s ≈ 20 × 10⁻⁶ is observed in as-prepared Fe₄₇Ni₂₇Si₁₁B₁₃C_2, while low and negative λ_s ≈ −0.3 × 10⁻⁶ is obtained for Co₆₇Fe_3.9Ni₁.₅B₁₁.₅Si_14.5Mo_1.6 microwire. Annealing affects the magnetostriction coefficients and Curie temperatures, T_c, of both Fe₄₇Ni₂₇Si₁₁B₁₃C₂ and Co₆₇Fe_3.9Ni₁.₅B₁₁.₅Si_14.5Mo_1.6 glass-coated microwires in a similar way. Observed dependencies of hysteresis loops, λ_s and T_c on annealing conditions are discussed in terms of superposition of internal stresses relaxation and structural relaxation of studied microwires. We observed linear λ_s 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. Full article

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. Full article

In this article, we study the effect of annealing temperature and applied stress on the magnetic properties of ${\mathrm{Fe}}_{71.80}{\mathrm{B}}_{13.27}{\mathrm{Si}}_{11.02}{\mathrm{Nb}}_{2.99}{\mathrm{Ni}}_{0.92}$ and ${\mathrm{Co}}_{65.34}{\mathrm{Si}}_{12.00}{\mathrm{B}}_{10.20}{\mathrm{Cr}}_{8.48}{\mathrm{Fe}}_{3.90}{\mathrm{Mo}}_{0.08}$ 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. Full article

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. Full article

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 (D_g = 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. Full article

In the current study we have obtained Co₂FeSi glass-coated microwires with different geometrical aspect ratios, ρ = d/D_tot (diameter of metallic nucleus, d and total diameter, D_tot). The structure and magnetic properties are investigated at a wide range of temperatures. XRD analysis illustrates a notable change in the microstructure by increasing the aspect ratio of Co₂FeSi-glass-coated microwires. The amorphous structure is detected for the sample with the lowest aspect ratio (ρ = 0.23), whereas a growth of crystalline structure is observed in the other samples (aspect ratio ρ = 0.30 and 0.43). This change in the microstructure properties correlates with dramatic changing in magnetic properties. For the sample with the lowest ρ-ratio, non-perfect square loops are obtained with low normalized remanent magnetization. A notable enhancement in the squareness and coercivity are obtained by increasing ρ-ratio. Changing the internal stresses strongly affects the microstructure, resulting in a complex magnetic reversal process. The thermomagnetic curves show large irreversibility for the Co₂FeSi with low ρ-ratio. Meanwhile, if we increase the ρ-ratio, the sample shows perfect ferromagnetic behavior without irreversibility. The current result illustrates the ability to control the microstructure and magnetic properties of Co₂FeSi glass-coated microwires by changing only their geometric properties without performing any additional heat treatment. The modification of geometric parameters of Co₂FeSi glass-coated microwires allows to obtain microwires that exhibit an unusual magnetization behavior that offers opportunities to understand the phenomena of various types of magnetic domain structures, which is essentially helpful for designing sensing devices based on thermal magnetization switching. Full article

We used the Taylor–Ulitovsky technique to prepare nanocrystalline Co₂MnGe Heusler alloy glass-coated microwires with a metallic nucleus diameter of 18 ± 0.1 µm and a total diameter of 27.2 ± 0.1 µm. Magnetic and structural studies were carried out to determine the fundamental magneto-structural characteristics of Co₂MnGe glass-coated microwires. XRD revealed a well-defined nanocrystalline structure with an average grain size of about 63 nm, lattice parameter a = 5.62 and a unique mixture of L2₁ and B2 phases. The hysteresis loops measured at different temperatures indicated a well-known ferromagnetic behavior for the reduced remanent, where a monotonic increasing in the reduced remanent and saturation magnetization occurs. The coercivity shows anomalous behavior compared to the Co2Mn-based glass-coated microwires. The magnetization curves for field cooling and field heating (FC–FH) demonstrate a considerable dependence on the applied magnetic field, ranging from 50 Oe to 20 kOe. Internal stresses, originated by the production process, resulted in various magnetic phases, which were responsible for the notable difference of FC and FH curves on magnetization dependence versus temperature. Furthermore, the ferromagnetic behavior and expected high Curie temperature, together with high degree of the L2₁ order, make it a promising candidate for many applications. Full article

In the current study, we concentrated on the influence of annealing on the magnetic behavior of Co₂MnSi-based Heusler microwires. We set the annealing temperature at 1023 K for 2 h, as the sample did not show any significant changes in the magnetic properties at lower temperatures, while annealing at temperatures above 1023 K damages the glass coating. Strong in-plane magnetocrystalline anisotropy parallel to the microwire axis was evident in the magnetic behavior at room temperature for as-prepared and annealed samples. The coercivity of the annealed sample was four times higher than that of the as-prepared sample across a wide range of measuring temperatures. Both annealed and as-prepared samples exhibit quite stable coercivity behavior with temperature, which may have interesting applications. The an nealed sample did not exhibit magnetic saturation for M-H loops measured below 50 K. Sharp irreversible magnetic behavior has been detected for annealed samples at a blocking temperature of 220 K; at the same time, the blocking temperature for the as-prepared sample was 150 K. The strong internal mechanical stress induced during the fabrication of Co₂MnSi microwires in addition to the internal stress relaxation caused by the annealing induced the onset of magnetic phases resulting in unusual and irreversible magnetic behavior. Full article

We study the effect of annealing and the applied magnetic field from 50 Oe to 20 kOe on the magneto-structural behavior of Ni₂FeSi-based Heusler microwires fabricated by using Taylor-Ulitovsky technique. Using the XRD analysis, a strong effect of annealing, manifested as the development of the crystallization process, was observed. The average grain size and crystalline phase content of annealed sample increase from 21.3 nm and 34% to 32.8 nm and 79%, respectively, as-compared to the as-prepared one. In addition, upon annealing, phase transforms into a monoclinic martensitic structure with a modulation of 10 M, which cannot be found in the as-prepared sample. Concerning the magnetic properties, both samples show ferromagnetic behavior below and above the room temperature, where the Curie temperature of Ni₂FeSi is higher than the room temperature. The induced secondary phases have a noticeable effect on the magnetic behavior of the annealed sample, where a high normalized saturation magnetization (NM_s) and low normalized reduced remenance (M_r = M/M_5K), compared to the as-prepared have been detected. Additionally, the coercivity of annealed sample shows one flipping point at 155 K where its behavior changes with temperature. Meanwhile, the as-prepared sample show two flipped point at 205 K and 55 K. A mismatch between field cooling (FC) and field heating (FH) magnetization curves with temperature has been detected for annealed sample at low applied magnetic field. The difference in magnetic and structure behavior of Ni₂FeSi microwires sample is discussed considering the effect of induced internal stresses by the presence of a glass coating and the recrystallization and stresses relaxation upon annealing. Full article

In this work, we have successfully fabricated nanocrystalline Co₂MnSi Heusler alloy glass-coated microwires with a metallic nucleus diameter (d_nuclei) 10.2 ± 0.1 μm and total diameter 22.2 ± 0.1 μm by the Taylor–Ulitovsky technique for the first time. Magnetic and structural investigations have been performed to clarify the basic magneto-structural properties of the Co₂MnSi glass-coated microwires. XRD showed a well-defined crystalline structure with a lattice parameter a = 5.62 Å. The room temperature magnetic behavior showed a strong in-plane magnetocrystalline anisotropy parallel to the microwire axis. The M-H loops showed unique thermal stability with temperature where the coercivity (H_c) and normalized magnetic remanence exhibited roughly stable tendency with temperature. Moreover, quite soft magnetic behavior has been observed with values of coercivity of the order of H_c = 7 ± 2 Oe. Zero field cooling and field cooling (ZFC-FC) magnetization curves displayed notable irreversible magnetic dependence, where a blocking temperature (T_B = 150 K) has been observed. The internal stresses generated during the fabrication process induced a different magnetic phase and is responsible for the irreversibility behavior. Moreover, high Curie temperature has been reported (Tc ≈ 985 K) with unique magnetic behavior at a wide range of temperature and magnetic fields, making it a promising candidate in magnetic sensing and spintronic applications. Full article

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, D_g = 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 (T_B = 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 (T_c ≈ 1059 K), which predisposes this material to being a suitable candidate for high temperature spintronic applications. Full article

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. Full article