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

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05 April 2023

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06 April 2023

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Abstract
In current study we have obtained Co2FeSi-glass coated microwires with different geometrical aspect ratio, ρ = d/Dtot (diameter of metallic nucleus, d and total diameter, Dtot). The structure and magnetic properties are investigated at a wide range of temperature. XRD analysis illustrates a notable changing in the microstructure by increasing the aspect ratio of Co2FeSi glass coated microwires. 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 at 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 addition heat treatment. The modification of geometric parameters of Co2FeSi glass-coated microwires allows to obtain microwires which 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.
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Subject: Chemistry and Materials Science  -   Electronic, Optical and Magnetic Materials

1. Introduction

The use of ferromagnetic materials in spintronic applications has garnered increasing attention in recent years due to their unique magnetic properties that enable the control and manipulation of spin currents. Among the different types of ferromagnetic materials, micro/nano-structured materials have emerged as a promising candidate for enhancing spintronic devices' performance [1,2,3,4,5,6,7,8,9]. One of the most promising multidisciplinary research fields is spintronics, which enables the creation of the next-generation of nano & micro devices with improved processing and memory capability while consuming less power [10]. To address the various required criteria, such as high spin polarization or high Curie temperature, Tc, a new generation of materials with multifunction uses has to be created [11]. The Heusler compounds are one of the potential smart materials with desirable characteristics for spintronic and magneto-electronic applications [12]. Perfect lattice matching with major substrates, high Tc above room temperature, and intermetallic controllability for spin density of states at the Fermi energy level—where approximately 100% of spin polarized near the Fermi level is reported [11,12,13,14,15]—are just a few of their advantages.
In terms of half-metallic alloys, Co2-based full-Heusler compounds are among the most promising ones because of their high thermal stability, high Curie temperatures (Tc ≈1100 K) for the bulk sample, high magnetic moment (~ 6 µB/f.u.), and low Gilbert damping constant ( α = 0.004) [14,16,17]. They also have exotic transport properties, an electric structure determined by ab initio calculations [16], and high magnetic moments. The significant anomalous Hall effect that Co2-based Heusler compounds exhibit because to the enormous Berry curvature associated with their band structure is also of current interest [16,18]. These factors have the scientific community interested in Co-based full-Heusler alloys. These types of alloys are therefore extensively researched in several configurations, including nanoparticles [19], thin films [15,17,20], and nano/micro wires [21,22,23,24]. It is important to note that the fabrication of Heusler alloys nanoparticles and thin films faces numerous difficulties for application purposes, including the high cost of preparation methods, chemical composition inhomogeneity, and ease of oxidation from the perspective of proper atomic ordering and material chemistry [20]. The diffusion of substrate atoms into the film results in the existence of atomic disorder and phase separations, which are commonly observed [25], in addition to the lattice mismatch between the alloy and the substrate. Furthermore, in order to start the requisite structural ordering, the arc-melted or thin-film formed Heusler alloys need lengthy, high temperature annealing procedures [26].
Magnetic wires research has received a lot of interest during the last several decades [27]. The focus is on amorphous magnetic wires, which can exhibit unusual magnetic features such as spontaneous magnetic bistability or the Giant magnetoimpedance phenomenon [27,28]. Several manufacturing processes involving fast solidification can be used to create magnetic wires containing amorphous and/or nanocrystalline phases [27,28]. Nevertheless, only the Taylor-Ulitovsky manufacturing approach allows the preparation of magnetic microwires with the widest diameter range (from 0.2 to 100 µm) [27,28]. Such microwires are composites consisting of metallic nucleus (with 0.2 ≤d ≤100 µm) usually comprised of iron, cobalt, nickel or their alloys, covered by thin, flexible and insulating glass (typically Pyrex or Duran) coating (typically with thickness from 0.5 to 10 µm) [27,28]. As a result, the prospective applications of glass-coated microwires in sensing, actuation, and biomedical engineering have been expanded. The insulating and flexible glass coating protects the microwires from oxidation, corrosion, and other environmental factors while simultaneously giving them outstanding mechanical stability. Moreover, the glass layer and the magnetically flexible amorphous metallic nucleus provide high sensitivity to external stimuli including magnetic fields, temperature fluctuations, and mechanical stress. [27,28,29,30,31,32,33,34,35]. Such sensitivity is connected to the ferromagnetic origin of the metallic nucleus, which responds to the applied stimulus. Innovative sensors that monitor magnetic fields, temperature, and stress have been developed using glass-coated microwires for a range of applications [27,28,29]. Additionally, they have shown potential characteristics for actuators and in medical applications, including as cancer treatment and medicine administration. Future technological advancements can use glass-coated microwires because of their distinctive combination of properties [27,29].
In this article, we report an attempt to prepare Co2FeSi glass-coated microwires with variable geometrical aspect ratios ρ = d/Dtot ( being d-diameter of metallic nucleus and Dtot - total diameter). The fabrication method was chosen because of the intriguing magneto-structural behavior of glass-coated microwires derived from Heusler alloys, as well as functional properties of glass-coated microwires such as superior mechanical properties, insulating, thin and flexible glass-coating, and thin dimensionality [27,29,30,31,32,33,34,35]. As a result, we have prepared Co2FeSi glass-coated microwires using the Taylor-Ulitovsky procedure, which is detailed previously [27,36,37]. The Taylor-Ulitovsky approach, which has been utilized since the 1960s [36], is one of the current fabrication methods used to make Heusler alloys glass-coated microwires with a wide variety of geometric characteristics [21,22,24,27,28,29,30,31,32,33,34,35]. The primary benefit of this low-cost technique is that it allows the production of thin and long (a few kilometers long) microwires with a wide diameter range (d- values ranging from 0.2 to 100 µm) at high speeds (up to a few hundred meters per minute) [36,37,38]. This process is also used to prepare glass-coated microwires with excellent mechanical properties [21,39,40,41]. Glass coating on microwires can give us with extra benefits such as better insulation and environmental protection. Moreover, the availability of a biocompatible thin, flexible, insulating, and highly transparent glass coating may aid biological applications [29,42,43]. As a result, Heusler microwires based on Co2FeSi are a potentially smart material with applications in a wide range of devices. To the best of our knowledge, up to date no one has reported on the production and structural, mechanical, or magnetic characterization of Co2FeSi-based glass-covered Heusler microwires with varied ρ - ratios, as well as the investigation of its influence on magneto-structure behavior.

2. Materials and Methods

Arc melting is a method of manufacturing Co2FeSi alloys that involves melting the precursor components together in an electric arc furnace. Typically, the following procedures are used to create Co2FeSi alloys by arc melting: i) preparing the precursor ingredients. The precursor elements for the Co2FeSi alloy are weighed and deposited in a graphite crucible, containing cobalt (99.99%), iron (99.9%), and silicon (99.99%). ii) The materials melting. The crucible containing the precursor materials is put in an electric arc furnace, and an electrical current is fed through the materials to start the melting process in a vacuum and argon atmosphere. The furnace temperature is precisely regulated to ensure that the ingredients melt and mix equally. iii) The cooling and solidification processes. The crucible is withdrawn from the furnace and allowed to cool once the components have melted and combined. The Co2FeSi alloy (ingot) is created as the ingredients consolidate. This process were then repeated five times to achieve perfect homogeneity and a homogeneous microstructure. Once the Co2FeSi alloy has solidified and formed an ingot, the ingot is used to prepare Co2FeSi glass-coated microwires using the Taylor-Ulitovsky process. As described in the introduction, the Taylor-Ulitovsky preparation technique offers significant benefits over alternative procedures for manufacturing glass-coated microwires. One advantage is that it enables the fabrication of microwires with very thin glass coatings, generally up to a few micrometers thick. This thin covering permits the electrical and magnetic characteristics of the microwire metallic nucleus to be preserved, making the resultant microwires valuable for a wide range of applications. Many prior publications [21,22,24,27,28,29,30,31,32,33,34,35] explain the manufacturing method in detail. A glass capillary was produced and filled with molten Co2FeSi alloy after a high frequency inductor heated an ingot over its melting temperature. The diameter of the metallic nuclei, d, was then determined by varying the speed of wire drowning and the rotation of the pick-up bobbin. The manufactured microwire is sent via a coolant stream to complete the fast melt quenching process.
We used Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) (JEOL-6610LV, JEOL Ltd., Tokyo, Japan) to determine the aspect ρ -ratio of Co2FeSi glass-coated microwires samples and its related nominal chemical composition.
The XRD structure analysis was carried on by using X-ray diffraction (XRD) BRUKER (D8 Advance, Bruker AXS GmbH, Karlsruhe, Germany).
The magnetic behavior was studied through two different ways: hysteresis loops at temperatures between 5 and 350 K, and thermomagnetic curves following three different protocols, zero field cooling (ZFC), field cooling (FC) and field heating (FH) at low magnetic field ( H = 200 Oe). All magnetization curves were measured using a PPMS (Physical Property Magnetic System, Quantum Design Inc., San Diego, CA) vibrating-sample magnetometer at temperatures, T, between 5 and 400 K for ZFC, FC and FH magnetic curves. For the hysterics loops we only focus on the in-plane configuration where the applied magnetic field is parallel to the wire axis. The results are provided in terms of the normalized magnetization, M/M5K, where M5K is the magnetic moment obtained at 5 K to avoid the misleading of the errors estimation in the estimation of the magnetization saturation values.

3. Results

3.1. Analysis of Chemical and Structural Data

The geometries (ρ-ratios) and chemical compositions of prepared samples are shown in Table 1. Using the EDX data from Table 1, it was revealed that the metallic nucleus composition differed considerably from the stoichiometric one (Co2FeSi). The features of the preparation process, which involved alloy melting and casting, were the cause of this slight variation. To quantify the difference, we checked at the nominal composition for 8 sites as illustrated in Figure 1a. An atomic average of Co44Fe23Si33 was used to confirm that the true 2:1 ratio of Co and Fe applied in all sites. A high Si ratio was found because of the interfacial layer that exists between the metallic nucleus and the glass covering.
In order to study the order state of our produced Co2FeSi Glass coated microwires, and to elucidate the effect of the aspect ratio modification on the crystalline structure, XRD structure analysis was carried on by using X-ray diffraction (XRD).
As illustrated in Figure 2 the changing in the geometric ρ-ratio has a strong influence on the structure of Co2FeSi glass-coated microwires. For the sample with the lowest ρ- ratio, i.e. ρ = 0.25, the sample shows an amorphous structure where no crystalline peaks is detected. The wide halo at 2Ө = 22.3° is related to the glass coating layer, as reported in our previous works [21,22,24,27,28,29,30,31,32,33,34,35]. By increasing the geometric aspect ratio a crystalline structure of metallic nucleus becomes evident with a notable peak at 2Ө = 46.2°, attributed to the (220) reflection. Further increase of geometric ρ-ratio results in the perfect crystalline structure of studied samples, where the crystalline peak intensity increases and additional peak appears at 2Ө = 85.4°, corresponding to the (422) reflection. The analysis of XRD profiles of the two crystalline Co2FeSi samples, i.e. GCMWC (P = 0.30) and GCMWB (P = 0.43), indicates an A2 single-phase structure with a small tetragonal distortion (traces of tetragonal martensite phase), and a broadened peak around 22⁰ attributed to an amorphous state for GCMWC and mixed L21 or B2 phases with amorphous state for GCMWB sample [34,35].
The (220) and (422) reflections in GCMWC sample are split due to some tetragonal distortions of the crystal lattice. A similar phenomenon was seen and discussed elsewhere [44]. It is known, that a split in the brag diffraction patterns lead to a small distortion of the crystalline structure [45]. The absence of a (400) peak around 85⁰, which is expected to be present in the A2 structure, increases the possibility that the crystallites are too fine to be detected by X-rays, as reported elsewhere [46]. In addition, the absence of some peaks can be caused by a similar scattering factor of the constituent elements (Co, Fe, and Si) [47]. Otherwise, according to the theoretical outcomes of Zhang et al., the disordered A2 state is more energetically preferable than those of the ordered L21 or B2 phases [48,49]. Nevertheless, the well-defined and sharp diffraction patterns in this sample (GCMWC sample) indicate a high crystallinity, as-compared with the other two XRD spectrum. As the the development of traces of secondary phase (tetragonal martensite) can affect the magnetic behavior, this will be explored in more details in the following sections.
We estimated the lattice parameters of the two crystalline Co2FeSi glass-coated microwires and then we employed the Debye- Scherrer's equation, as presented in our previous work [23], to investigate the microstructure of Co2FeSi in greater depth. Using this methodology, we can estimate the average grain size, Dg, associated to the principal peaks, which is approximately 37.6 nm and 45.8 nm for GCMWB and GCMWC of Co2FeSi microwires, respectively as illustrated in Table 2.

3.2. Magnetic Characterization

3.2.1. Room Temperature Magnetic Properties

Figure 3 shows the magnetic hysteresis loops of Co2FeSi glass-coated microwires with different ρ- ratios, obtained at room temperature with an applied magnetic field parallel to the microwire axis. All samples exhibit typical ferromagnetic behaviour, due to the high Curie point of Co2FeSi alloy greater than 1100 K [46]. The sample with low ρ -ratio exhibits soft magnetic properties with coercivity, Hc, around 14 Oe and non-square hysteresis loop shape (Figure 3a). However, the sample with the largest ρ -ratio shows almost perfectly square hysteresis loops with higher Hc (about 87 Oe), than Co2FeSi with low ρ -ratio (see Figure 3b and 3c). In addition, the hysteresis loop shows multistep magnetic behavior (indicated with arrows in figure 3c). The almost square hysteresis loops for the GCMWC microwire with normalized remanent, Mr, near to 0.96 indicates the axial character of magnetic anisotropy with easy axis of magnetization along the direction of applied magnetic field. Thus, the increase in ρ - ratio affects the magnetocrysttaline ansiotropy and its direction has the same direction of (220) and (420), as illustrated in the structural section. However, in the sample GCMWB with crystaline structure, non-perfectly square loops is observed. Such change in the hysteresis loop shape must be related to the presence of the considerable amount of amorphous phase beside the disordered B2 or little ordered L21 structures. In our previous work at the same alloys, but with low ρ – ratio (ρ = 0.26), the enhancement of the magnetocrystlline anisotropy, the squareness and coercivity of Co2FeSi glass coated microwires after annealling was observed [21,22,24]. As we illustated in our previous work, the main two factors affecting the magnetic anisotropy behavior in Heusler based glass- coated mixcrowires are unixial magnetic anisotropy and cubic magnetocrystalline anisotropy [21,22,24]. By increasing the ρ-ratio an enhacement in the crystalline phase content correlates with the magnetic properties modification, i.e. the main factor controlling the magnetic anistropy is the cubic magnetocrystalline anistropy. Unfortunately, currently we are not able to measure this type of anisotropy experimentaly, but the perfectly square loop indicates its stronge effect for the GCMWB and GCMWC samples. As seen in Figure 4, the GCMWc sample shows the highest anisotropy field Hk, coercivity Hc and normalized remenant Mr.

3.2.2. Thermomagnetic Properties

It is worth noting that the ferromagnetic materials temperature stability is a crucial characteristic for their possible applications in spintronic and sensing devices. Hence, for a wide range of measurement temperatures, 5-350 K, we investigated the magnetic behavior of Co2FeSi glass coated microwires with different ρ- ratios. The shape of the loops follows the same trend observed at room temperature: non-square for the GCMWA sample, quite square for the GCMWB one, and almost square for the GCMWC one (loops not shown) In Figure 5, the evolution of Hc and Mr with the temperature is shown. This behavior demonstrates that for the GCMWC sample, cubic magnetocrystalline anisotropy prevails up to 350 K.
By analyzing the hystersis loops measured at temperature range , 5–350 K of Co2FeSi glass-coated microwires with different ρ- ratio, an interesting magnetic behavior is found for both the temperature dependence of Hc and of the normalized remanence, Mr. GCMWC sample shows the highest value of the coercivity at the all measuring range of temperature range, with an average value of Hc 6 times higher than those of the GCMWA and GCMWB samples. Both GCMWA and GCMWB samples show quite similer values of the Hc where the different between the average value of coercivity is about 2 Oe. By estimating the differences of the coercivity (ΔHc) between the maximum value of coercivity (Hc (max)) and the lowest value of the coercivity (Hc (min)) for all samples we pretend to show its stability with temperature. The samples with a clear crystalline phase, GCMWB and GCMWC samples, show higher temperature stability than the amorphous GCMWA sample: Hence the ΔHc is 3.5 and 9 Oe for GCMWB and GCMWC samples, respectivly, whereas ΔHc is 15 Oe for the GCMWA one. The magnetic stability is more clear in the case of Mr tendency with temperature of Co2FeSi glass-coated microwires with different ρ - ratios. As shown in Figure 5b, both GCMWB and GCMWC samples show high stability with temperature, with ΔMr 0.05 and 0.06, respectivily (see Table 3). Meanwhile, the behavior of Mr of GCMWA is rather different, comparing to the other samples with higher ρ -ratios, where a monotonic increase with decreasing the temperature has been observed.
Figure 6 shows the complete thermomagnetic behavior of Co2FeSi glass-coated microwires with different ρ -ratios. We performed the ZFC, FC and FH magnetic temperature dependence to check any possible phase transition. Thus, the measurements were performed at low magnetic field 200 Oe. For GCMWA sample, the ZFC, FC and FH magnetizations curves show non-homogonous behavior, beside an irreversible magnetic behavior at T = 150 K. Such irreversibility has been observed in our previous work dealing with Co2FeSi-based glass-coated microwires with aspect ratio ρ = 0.26, (see [21,22,24].). In this works we have illustrated that the irreversibility enhanced by preforming annealing at 873 K and 973 K for 1 h. The induced martensitic transition and the changing in the internal stresses associated with the glass-covering layer with temperature allow to control the irreversibility behavior. The interesting point for Co2FeSi-glass-coated microwires with the lowest ρ- ratio, i.e., ρ = 0.23, is that its blocking temperature is observed at T = 150 K, like the Co2FeSi-glass-coated microwires with ρ = 0.26 [21,22,24]. For GCMWA sample, which is totally in amorphous state (see Figure 2), the main reason for the irreversibility behavior is the strong internal stress induced by the glass covering layer. For GCMWB and GCMWC sample, i.e., increasing ρ -ratio, the irreversibility behavior disappeared and the usual ferromagnetic behavior is observed with homogenous ZFC, FC and FH magnetic curves. The homogenous magnetization curves are due to the induced crystal structure with A2-type and B2 or L21 cubic structure for GCMWC and GCMWB, respectively.
We believe that increasing the ρ - ratio of Co2FeSi glass-coating microwires affects recrystallization, atomic ordering, and stress reduction. Furthermore, for samples with a high ρ -ratio, the induced L21/B2 and A2 cubic structure types generate a strong magneto crystalline anisotropy, explaining the the behavior of magnetic properties such as Hc, Mr, Hk, and thermomagnetic curves with temperature. In fact, as shown in several previous publication, the internal stresses values are affected by the ρ – ratio: the lower the ρ – ratio, the higher the internal stresses related to the presence of the glass-coating [50,51,52]. On the other hand, the glass-coating thermal conductivity can affect the quenching rate of the metallic nucleus: lower quenching rate must be at the origin of higher crystallinity of the microwires with relatively thick glass-coating [27].
Resuming, Co2FeSi-glass-coated microwires are an excellent candidate for a wide range of industrial applications, and specially for sensors, due to their perfect squared loops at a wide temperature range and homogenous thermomagnetic behavior with temperature.

5. Conclusions

In summary, we have fabricated Co2FeSi glass-coated microwires with different geometrical aspect ratios. A strong influence of the geometric aspect ratio on the magnetic and structural properties is observed and discussed. The increase in the aspect ratio correlates with the increasing degree of crystallinity. Promising coercivity and normalized remnant stability with temperature are found for Co2FeSi-glass coated microwires with a high aspect ratio. For the sample with the lowest aspect ratio, the thermomagnetic curves show large irreversibility with a blocking temperature of T = 150 K. The induced crystal structure of the A2-type gives rise to a high cubic magnetocrystalline anisotropy that controls the magnetic behavior of Co2FeSi glass-coated microwires and makes it a suitable candidate for magnetic sensing.

Author Contributions

Conceptualization, M.S. and A.Z.; methodology, V.Z.; validation, M.S., V.Z. and A.Z.; formal analysis, M.S and A.W.; investigation, M.S., A.W, and A.Z.; resources, V.Z. and A.Z.; data curation, M.I; writing—original draft preparation, M.S., A.W. and A.Z.; writing—review and editing, M.S., R.A.L and A.Z.; visualization, M.S., A.W., and M.I; supervision, R.A.L and A.Z.; project administration, V.Z. and A.Z.; funding acquisition, V.Z., and A.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Spanish MICIN, under PID2022-141373NBI00, by EU under “INFINITE” (Horizon Europe) project and by the Government of the Basque Country, under PUE_2021_1_0009 and Elkartek (MINERVA, ZE-KONP and MAGAF) projects and by under the scheme of “Ayuda a Grupos Consolidados” (Ref.: IT1670-22). MS wish to acknowledge the funding within the Maria Zambrano contract by the Spanish Ministerio de Universidades and European Union –Next Generation EU (“Financiado por la Unión Europea-Next Generation EU”). We also wish to thank the administration of the University of the Basque Country, which not only provides very limited funding, but even expropriates the resources received by the research group from private companies for the research activities of the group. Such interference helps keep us on our toes.

Institutional Review Board Statement

“Not applicable.”.

Informed Consent Statement

“Not applicable.”.

Data Availability Statement

“Not applicable.”.

Acknowledgments

The authors are thankful for the technical and human support provided by SGIker of UPV/EHU (Medidas Magnéticas Gipuzkoa) and European funding (ERDF and ESF).

Conflicts of Interest

“The authors declare no conflict of interest.”.

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Figure 1. The cross section of selected Co2FeSi glass-coated microwires with aspect ratio 0.30 images (a) and the chemical composition spectra of EDX of one of the points (b).
Figure 1. The cross section of selected Co2FeSi glass-coated microwires with aspect ratio 0.30 images (a) and the chemical composition spectra of EDX of one of the points (b).
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Figure 2. XRD analysis of Co2FeSi glass-coated microwires with different aspect ratio measured at room temperature. The inset of Figure 2 indicates the A2-type cubic structure.
Figure 2. XRD analysis of Co2FeSi glass-coated microwires with different aspect ratio measured at room temperature. The inset of Figure 2 indicates the A2-type cubic structure.
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Figure 3. Room temperature hysteresis loops for Co2FeSi glass-coated microwires (a) GCMWA, (b) GCMWB and (c) GCMWC. The arrows in Figure 3 (c) pinpoints the multistep magnetic behavior.
Figure 3. Room temperature hysteresis loops for Co2FeSi glass-coated microwires (a) GCMWA, (b) GCMWB and (c) GCMWC. The arrows in Figure 3 (c) pinpoints the multistep magnetic behavior.
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Figure 4. Aspect ratio dependence on coercivity (Hc), normalized remanence (Mr), and in –plane anisotropy field (Hk) of Co2FeSi glass-coated microwires (lines for eye guide).
Figure 4. Aspect ratio dependence on coercivity (Hc), normalized remanence (Mr), and in –plane anisotropy field (Hk) of Co2FeSi glass-coated microwires (lines for eye guide).
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Figure 5. Temperature dependence of the coercivity (a) and normalized remanence (b) of Co2FeSi glass-coated microwires with different aspect ratio (lines for eye guide).
Figure 5. Temperature dependence of the coercivity (a) and normalized remanence (b) of Co2FeSi glass-coated microwires with different aspect ratio (lines for eye guide).
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Figure 6. Temperature dependence of magnetization measured for Co2FeSi glass-coated microwires (a) GCMWA, (b) GCMWB and (c) GCMWC with applied external magnetic field 200 Oe.
Figure 6. Temperature dependence of magnetization measured for Co2FeSi glass-coated microwires (a) GCMWA, (b) GCMWB and (c) GCMWC with applied external magnetic field 200 Oe.
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Table 1. The geometrical parameters and average (Av.) of atomic percentage of Co, Fe and Si elemental composition in Co2FeSi glass-coated microwires.
Table 1. The geometrical parameters and average (Av.) of atomic percentage of Co, Fe and Si elemental composition in Co2FeSi glass-coated microwires.
Sample Aspect ratio (ρ) Chemical composition
GCMWA 0.23 Co44Fe23Si33
GCMWB 0.30 Co44Fe23Si33
GCMWC 0.43 Co44Fe23Si33
Table 2. The average grain size and lattice parameters of Co2FeSi glass-coated microwires with different aspect ratio.
Table 2. The average grain size and lattice parameters of Co2FeSi glass-coated microwires with different aspect ratio.
Sample Average grain size (nm) Lattice parameters
GCMWA - -
GCMWB 45.8 5.63
GCMWC 37.6 2.81
Table 3. The geometrical parameters and average (Av.) of Co2FeSi glass-coated microwires with different aspect ratio.
Table 3. The geometrical parameters and average (Av.) of Co2FeSi glass-coated microwires with different aspect ratio.
Sample ΔHc (Hc (max) - Hc (min)) ΔMr (Mr (max) – Mr (min))
GCMWA 15 ± 2 Oe 0.7 ± 0.1
GCMWB 3.5 ± 0.5 Oe 0.06 ± 0.01
GCMWC 9 ± 2 Oe 0.05 ± 0.01
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