Metallic Nucleus Diameter Research Articles

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.

Enhancing the Squareness and Bi-Phase Magnetic Switching of Co2FeSi Microwires for Sensing Application.

In the current study we have obtained Co2FeSi glass-coated microwires with different geometrical aspect ratios, ρ = d/Dtot (diameter of metallic nucleus, d and total diameter, Dtot). 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.

Preparation and Magneto-Structural Investigation of High-Ordered (L21 Structure) Co2MnGe Microwires

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.

Preparation and Magneto-Structural Investigation of Nanocrystalline CoMn-Based Heusler Alloy Glass-Coated Microwires

In this work, we have successfully fabricated nanocrystalline Co2MnSi Heusler alloy glass-coated microwires with a metallic nucleus diameter (dnuclei) 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 (Hc) 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 Hc = 7 ± 2 Oe. Zero field cooling and field cooling (ZFC-FC) magnetization curves displayed notable irreversible magnetic dependence, where a blocking temperature (TB = 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.

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.

Post-Annealing Influence on Magnetic Properties of Rapidly Quenched Ni–Mn–Ga Glass-Coated Microwires

In this article, we showed how the post-annealing process affects the magnetic properties of rapidly quenched Ni-Mn-Ga glass-coated microwires. Microwires with Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">63</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">25</sub> chemical composition, total diameter D = 54.6 μm and metallic nucleus diameter d = 26.7 μm, were prepared by the Taylor-Ulitovsky technique. The annealing temperature was fixed at 873 K, and the time was 1 and 10 h. The microwires were slowly cooled to room temperature after annealing. Based on thermomagnetic curves and hysteresis loops, we suggest crystallographic texture in the wires that considerably affect magnetic properties. The wires' internal structure indicates nanocrystalline state with radial micrometers and submicrometer grains distribution in the wire annealed during 10 h. A ferromagnetic-to-paramagnetic phase transition occurs around room temperature. No signs of a martensitic transformation were found. The difference in magnetization saturation, remanence, and Curie temperature values for 1- and 10-h annealed microwires indicates the influence of internal stresses and that created by the presence of a glass coating.

The effect of stress distribution in the bulk of a microwire on the magnetization processes

Abstract The effect of tensile stresses on the magnetic properties of amorphous microwires with positive magnetostriction has been studied. It has been determined that the experimental dependence of coercivity on the tensile stresses is reversible and consists of linear and square root parts. The evolution of an average stress level in the “core” and surface domain layer has been theoretically estimated depending on the external tensile stress. The value of internal stress level may vary from 150 to 600 MPa in “core” for microwires with different ratio of amorphous metallic nucleus diameter to thickness of glass shell. Crucial differences of tension of glass-coated and uncoated microwires have been investigated. The analysis of these differences with relation to effect under tension has been performed.

The effect of annealing on magnetic properties of “Thick” microwires

Abstract In this paper we provide results on effect of post-processing on magnetic properties (giant magnetoimpedance, GMI, effect and domain wall dynamics) of Fe71.7B13.4Si11Nb3Ni0.9 glass-coated microwire with metallic nucleus diameter d = 103 μm and total diameter D = 158 μm prepared by Taylor-Ulitovsky method. Amorphous structure of as-prepared wires is confirmed by X-ray diffraction and electronic microscopy. As-prepared glass-coated wires present relatively low GMI ratio (about 50% at 500 MHz) and relatively low coercivity (about 25 A/m). Additionally, as-prepared sample present rectangular hysteresis loop and fast single domain wall propagation with domain wall mobility of about 11,9 m2/As. After annealing (either under tensile stress or without stress) we observed considerable improvement of the GMI ratio (from 50% up to 220% at 200 MHz) and domain wall mobility up to 15,5 m2/As. Observed GMI effect and domain wall mobility improvement has been attributed to the stresses relaxation and creep anisotropy. We demonstrated that the Taylor-Ulitovsky technique is suitable for preparation of “thick” Fe based amorphous microwires with good magnetic properties and GMI effect suitable for industrial applications.

Magnetic properties of “thick” glass-coated Fe-rich microwires

We report on preparation and magnetic properties of Fe71.7B13.4Si11Nb3Ni0.9 glass-coated microwire with metallic nucleus diameter d = 103 μm and total diameter D = 158 μm prepared by Taylor-Ulitovsky method. Amorphous structure of as-prepared microwires is confirmed by X-ray diffraction. As-prepared glass-coated microwires present relatively high GMI effect (about 50%) and relatively low coercivity (about 25 A/m). Additionally, as-prepared sample present rectangular hysteresis loop and fast single domain wall propagation with domain wall mobility of about 11,9 m2/As. After annealing we observed considerable improvement of the GMI ratio (from 50% up to 100%). Observed GMI effect improvement has been attributed to the stresses relaxation. From aforementioned studies we can conclude that the Taylor-Ulitovsky technique allows us to obtain thick ferromagnetic microwires with good magnetic properties and GMI effect suitable for industrial applications.

Continuous control of a resistance in Co-rich amorphous ferromagnetic microwires during DC Joule heating

In this paper, we present the resistance measurements of the amorphous ferromagnetic Co-rich microwires (metallic nucleus diameters 15–30 μm) during Joule heating by direct current. The heating currents were provided by a programming power supply, which allowed setting up a different heating and cooling regimes. The Wheatstone bridge circuit was used for continuous resistance monitoring during the heating process. We observed the dependences of the microwire resistance versus the time and the applied power of heating for the samples having common composition Co69Fe4Cr4Si12B11 and different diameters. It was shown that the irreversible changes of the microwire resistance were occurred during heat treatment. The microwires have gone through a crystallization phase under linear varying power in the range between 0 and 4.5 W and their relative resistance reduced by up to 10% relative to the initial values. The one-time annealing run increases the relative resistance of the microwires samples from 0.1% to 1% at the various values of maximum power. The repeated heating processes result to the reversibility of the resistance values; in that case each value of maximum applied power provides finite rise of the microwire resistance value.

Effect of annealing on magnetic properties of Ni–Mn–Ga glass-coated microwires

Abstract

Monocrystalline Heusler Co2FeSi alloy glass-coated microwires: Fabrication and magneto-structural characterization

Large scale production of single crystalline phase of Heusler Co2FeSi alloy microwire is reported. The long microwire (∼1 km) with the metallic nucleus diameter of about 2 µm is characterized by well oriented monocrystalline structure (B2 phase, with the lattice parameter a = 5.615 Å). Moreover, the crystallographic direction [101] is parallel to the wire’s axis along the entire length. Additionally, the wire is characterized by exhibiting a high Curie temperature (Tc > 800 K) and well-defined magnetic anisotropy mainly governed by shape. Electrical resistivity measurement reveals the exponential suppression of the electron-magnon scattering which provides strong evidence on the half-metallic behaviour of this material in the low temperature range.

Internal stresses influence on magnetic properties of Ni-Mn-Ga Heusler-type microwires

The influence of internal stresses on magnetic properties of Ni-Mn-Ga glass-coated microwire was investigated. Microwires with Ni63Mn12Ga25 chemical composition, full diameter D = 54.6 μm and metallic nucleus diameter d = 26.7 μm, were prepared by Taylor-Ulitovsky technique. An analysis of a separate influence of stresses, generated during the solidification of metal and those induced by the difference between thermal expansion coefficients of metal and glass, on magnetic properties of Ni-Mn-Ga microwire was done. Carrying out the heat treatment for a different time reveals the influence of the first type of stress. Removing the glass coating show the influence of the second type of stress. To analyze a complex influence of stresses we performed a heat treatment of the microwire after glass coating removal. The coercive force, saturation and remanence magnetization and Curie temperature were compared to show stresses influence. The change of easy magnetization axis direction was found for microwire with removed glass coating. A difference in surface grain size was indicated in the annealed glass-coated microwire and microwire, annealed after glass removal.

The stress components effect on the Fe-based microwires magnetostatic and magnetostrictive properties

For glass-coated amorphous ferromagnetic Fe-based microwires both joint and separate effect of metallic nucleus diameter, d, and the ratio of metallic nucleus diameter to the total diameter of microwire in glass shell, d/D, on magnetic properties is investigated. Thereby the contribution of both shell-induced stresses, associated with the ratio of diameters, and internal nucleus stresses (residual, quenching), associated with the diameter of the nucleus are estimated. A strong and non-monotonic effect of the metallic nucleus diameter and metallic nucleus diameter/total microwire diameter ratio on magnetostatic and magnetostrictive properties was established. For analysis, we considered magnetically bi-stable microwires of “classic” Fe77.5Si7.5B15 alloy with positive magnetostriction coefficient.

Magnetoelastic properties of Co‐based amorphous ferromagnetic microwires

Vibrational magnetometry and small‐angle magnetization rotation methods have been used to study magnetoelastic properties of glass‐coated Co‐rich microwires of composition Co69Fe4Cr4Si12B11 with metallic nucleus diameter d = 55 μm and total diameter D = 80 μm. The saturation wire magnetization has been found to be Ms = 590 emu cm−3, the magnetostriction constant λs = −0.49 × 10−7, and the bare anisotropy field Ha = 0.24 Oe. The average value of the residual quenching stress has been estimated to be Δσ ≈ 137 MPa. The diagonal Zφφ component of the giant magnetoimpedance tensor turns out to be significantly dependent on the position along the wire axis. This can be attributed to a non uniformity of the residual stress distribution. It is shown that the measurement of the magnetic characteristics of the microwire enables one to estimate quantitatively the magnitude of the applied mechanical stress.

Tuning of Magnetic Properties of Ni-Mn-In-Co Heusler-Type Glass-Coated Microwires

We report on magnetic properties and structure of Heusler-type NiMnIn(Co) glass-coated microwires with metallic nucleus diameters ranging from 13 up to 23 µm and total diameters from 47 to 55 µm by prepared by the Taylor-Ulitovsky technique.

Magnetic properties of Ni-Mn-In-Co Heusler-type glass-coated microwires

We report on fabrication and magnetic properties of Heusler-type NiMnInCo glass-coated microwires with metallic nucleus diameters, d, from 13 up to 23 μm and total diameters, D, from 47 to 55 μm by the Taylor-Ulitovsky technique. Considerable dependence of magnetization on magnetic field below and in vicinity of Curie temperature can be related with two-phase structure or with the Hopkinson effect.

Transformation of magnetic domain structure in Co- and Fe-rich amorphous microwires

We report the results of a magneto-optical Kerr effect (MOKE) study of the formation and transformation of the surface domain structure in a series of Co- and Fe-rich microwires. The microwires, with a metallic nucleus diameter of 100μm and glass coating thickness of 20μm, were studied by highly sensitive MOKE microscopy in the longitudinal geometry. A wide variety of types of surface domain structures was found in two types of microwires examined.

Studies of thermal and magnetic properties of Fe-based amorphous and nanocrystalline glass coated microwires

We studied the influence of magnetoelastic energy on properties of nanostructured glass-coated microwires with soft magnetic behaviour (Finemet-type microwires of Fe70.8Cu1Nb3.1Si14.5B10.6 and Fe73.8Cu1Nb3.1Si13B9.1 compositions). The magnetoelastic energy, stored during the Finemet-type microwires fabrication, affected the hysteresis loops, coercivity and heat capacity of Finemet-type microwires. Hysteresis loops of all as-prepared microwires showed rectangular shape, typical for Fe-rich microwires. As expected, coercivity, HC, of as-prepared microwires increases with decreasing of the ratio ρ defined as the ratio between the metallic nucleus-diameter, d to total microwire diameter, D. On the other hand, the change of heat capacity in TC, ΔСр, exhibits increasing with the ratio ρ. This relationship holds for microwires in the as-prepared state as well as after annealing.

Microstructure and magnetic properties of FINEMET nanowires

FINEMET (Fe73.5Cu1Nb3Si13.5B9) glass-coated nanowires and submicron wires with metallic nucleus diameters (Φm) between 100 and 500 nm and the glass coating thickness (tg) of 5 μm are reported for the first time. The microstructure of annealed ultrathin glass-coated wires evolves into a nanocrystalline one (DO3 nanograins of 10–20 nm embedded into the residual amorphous matrix) after annealing at 550 °C and 600 °C for 60 min. Despite the similar size of the nanograins, the volume occupied by them relative to the total volume increases from 50%–53% after annealing at 550 °C to 63%–65% after annealing at 600 °C, due to the increase in their number. This is reflected in a more accurate manner in the domain wall velocity measurements than in variation of the magnetic characteristics such as M(H), relative magnetic permeability or switching field. The magnetically softest nanocrystalline phase is formed at larger values of annealing temperature (Ta) for thinner wires, since larger temperature is needed to grow a sufficient number of DO3 grains at distances below the exchange length among them.