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Article

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

by
Mohamed Salaheldeen
1,2,3,4,*,
Valentina Zhukova
1,2,4,
Mihail Ipatov
1,2 and
Arcady Zhukov
1,2,4,5,*
1
Department of Polymers and Advanced, Chemistry Faculty, University of Basque Country, UPV/EHU, 20018 San Sebastián, Spain
2
Department of Applied Physcs, Faculty of Engineering of Gipuzkoa, EIG, University of Basque Country, UPV/EHU, 20018 San Sebastián, Spain
3
Physics Department, Faculty of Science, Sohag University, Sohag 82524, Egypt
4
EHU Quantum Center, University of the Basque Country, UPV/EHU, 20018 San Sebastián, Spain
5
IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain
*
Authors to whom correspondence should be addressed.
Crystals 2023, 13(11), 1550; https://doi.org/10.3390/cryst13111550
Submission received: 23 September 2023 / Revised: 19 October 2023 / Accepted: 26 October 2023 / Published: 29 October 2023
(This article belongs to the Topic Advanced Magnetic Alloys)
Browse Figures
Versions Notes

Abstract

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

1. Introduction

Heusler alloys, characterized by their typical X2YZ (full-Heusler) or XYZ (half-Heusler) compositions, represent a category of multifunctional materials [1,2,3,4,5]. Extensive research has been devoted to investigating the properties of Heusler alloys due to their diverse range of properties, such as the shape memory effect, substantial magnetic-field-induced strain (MFIS), half-metallic behavior, giant magnetocaloric effect (MCE), and exchange bias [3,4,5,6,7,8,9]. Heusler alloys are suitable for a variety of applications owing to their characteristics, especially in the fields of magnetic cooling, actuators, and energy harvesting [10,11,12]. Numerous bulk Heusler alloys have been successfully synthesized over time, and their structural and physical characteristics have been extensively studied.
Arc melting, followed by additional thermal treatment, is the main technique used to produce Heusler alloys [2,3,10]. This method makes it possible to produce Heusler alloys in bulk form. However, miniaturization has been investigated as an alternative approach to improve the aforementioned characteristics of Heusler alloys [10]. The performance of Heusler alloys can be improved noticeably by minimizing the dimensions of the alloys. For instance, in the context of magnetic cooling applications, the surface-to-volume ratio can be enhanced to significantly improve the heat-exchange rate by using low-dimensional Heusler alloys.
In recent years, growing attention has been paid to the synthesis and investigation of different families of Heusler alloys with reduced dimensions, such as thin micro/nanowires, ribbons, nanoparticles, and thin films [13,14,15]. However, the inherent brittleness of Heusler compounds, including Co-, Fe-, and Ni-based full-Heusler alloys, poses a challenge for their fabrication using conventional metallurgical techniques. Consequently, significant efforts have been directed toward the development of novel fabrication methods for producing Heusler alloys in different physical forms for a specified application. These endeavors aim to overcome the limitations imposed by brittleness and explore the potential of low-dimensional Heusler alloys. Additionally, the preparation of composites incorporating Heusler alloys has emerged as a promising approach to address the aforementioned brittleness issue, becoming a topic of considerable interest in the development of this family of functional materials [3,10].
Rapid melt quenching has been recognized by scientists since the 1960s as a commonly used method to produe innovative materials with a variety of morphological characteristics, including amorphous or crystalline (micro/nanocrystalline) structures, as well as metastable phases with reduced dimensions [16,17]. Using this technology, it is possible to obtain alloys with specified chemical compositions using rapid solidification, obtaining materials with more effective mechanical, magnetic, and corrosion properties [18,19,20]. Rapid melt quenching techniques have been developed to produce ribbons, wires, flakes, microwires, composite microwires, and other materials. The chosen alloy’s phase diagram, the quenching conditions, and the geometry of the prepared materials are only a few of the specific fabrication features that are critical in determining the final structure of the materials that are produced.
As previously mentioned, crystalline rapidly quenched materials generally exhibit inferior mechanical properties compared to their amorphous counterparts [20]. However, other properties relevant to various applications, such as enhanced corrosion resistance and biocompatibility, are desirable [21]. Furthermore, the miniaturization of rapidly quenched materials has emerged as a challenge for numerous applications. Consequently, the development of preparation methods capable of meeting these expectations has garnered significant attention in recent years.
One particularly promising technology aiming at the miniaturization of rapidly quenched materials while simultaneously improving magnetic, corrosion, and mechanical properties is the Taylor–Ulitovsky technique [22,23,24]. This technique enables the fabrication of thin metallic microwires (typically ranging from 0.02 to 100 μm in diameter) coated with a layer of glass [23,24,25,26,27,28,29,30]. The resulting thin glass-coated microwires, with either amorphous or nanocrystalline structures, can exhibit excellent magnetic softness. Additionally, the thin glass coating imparts new functionalities, including enhanced mechanical and corrosion properties, favorable adhesion to polymeric matrices, and biocompatibility [31,32,33]. In this regard, a few successful endeavors have been made using either the in-rotating-water technique to fabricate wires [34] or the Taylor–Ulitovsky technique to prepare glass-coated microwires from Heusler alloys [35,36,37,38,39,40,41]. These advances represent significant progress in the preparation of Heusler alloys in low-dimensional forms and have opened up opportunities for further exploration.
One of the peculiarities of the Taylor–Ulitovsky technique is that it allows the preparation of metallic microwires coated with insulating glass by simultaneous rapid solidification from the melt. This manufacturing method is intrinsically linked with internal stresses arising mostly due to the difference in the thermal expansion coefficients of the glass coating and the metallic alloy [18,42,43,44]. The magnitude of the internal stresses, σi, correlates with the ratio, ρ, between the metallic nucleus diameter, dmetal, and the total diameter, Dtotal. In this way, σi can be modified by changing the ρ–ratio [42,44].
In this study, we present an endeavor to produce a set of glass-coated microwires based on the X2YZ composition. These microwires were designed with fixed geometric parameters and a high Curie temperature exceeding 900 K. The objective was to examine the impact of the uniform internal stress induced by the glass layer coating on the magnetic and structural behavior of the samples, utilizing the Taylor–Ulitovsky process. The selection of this fabrication method was driven by the intriguing magneto-structural characteristics exhibited by glass-coated microwires derived from Heusler alloys, along with the advantageous functional properties associated with such microwires. We chose a series of Heusler alloys, i.e., Ni2FeSi, Co2FeSi, and Co2MnSi, with a high Curie temperature, which have a significant contribution in advanced spintronic applications due to their unique physical, electronic, and magnetic properties [2,12,14,17]. A strong dependence of the magnetic and structural properties of X2YZ-based glass-coated microwires on fixed geometric parameters was observed, and this reveals the sensitivity of the internal stress to the microstructure ordering and the chemical composition of the metallic nuclei of X2YZ-based glass-coated microwires.

2. Materials and Methods

The experimental conditions for the preparation Ni2FeSi, Co2FeSi, and Co2MnSi in bulk and glass-coated microwires are described in detail in our previous works [12,14,17]. The key point and objective of the current study is to fabricate the samples with fixed geometric parameters to investigate the effect of the internal stresses originated by the covering glass layer on the magnetic properties and microstructure in different series of X2YZ-based full-Heusler glass-coated microwires.
The following procedures were used to prepare Ni2FeSi, Co2FeSi, and Co2MnSi alloys by arc melting. The precursor elements for the Ni2FeSi, Co2FeSi, and Co2MnSi alloys were weighed to fit with the nominal ratio (X)2:(Y)1:(Z)1) and deposited in a graphite crucible, containing Ni (99.99%), Co (99.99%), Fe (99.9%), Mn (99.99%), and Si (99.99%). The ingots of Ni2FeSi, Co2FeSi, and Co2MnSi alloys (ingot) were created by combining the ingredients. For all alloys, the melting process was repeated five times to make the alloys homogenous. The chemical compositions and the nominal ratio of the X2YZ alloys were tested before proceeding to the glass-covering process. By using the Taylor–Ulitovsky technique, we can obtain a wide range of Heusler-based glass-coated microwires with proper dimensions and length depending on the application and the purpose of the investigations [22,26,37,41,42,43,44,45,46,47]. Controlling the casting process rate of the melting ingot, i.e., Ni2FeSi, Co2FeSi, and Co2MnSi, enabled us to obtain glass-coated microwires with a fixed nuclei diameter and well-controlled thickness of the covering glass layer. Thus, fixed geometric parameters were easily obtained in the current alloys. After preparation of the Ni2FeSi, Co2FeSi, and Co2MnSi MWs, we estimated the geometrical parameters dmetal (µm), Dtotal (µm), and the aspect ratio (ρ = dmetal/Dtotal) by using an optical microscope and Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) (JEOL-6610LV, JEOL Ltd., Tokyo, Japan) to determine the geometric parameters of the Ni2FeSi, Co2FeSi, and Co2MnSi MW samples and their related nominal chemical compositions (see Table 1). After confirming the nominal ratio and the chemical compositions of the Ni2FeSi, Co2FeSi, and Co2MnSi MWs, microstructure analysis was performed at room temperature by using X-ray diffraction (XRD) (D8 Advance, Bruker AXS GmbH, Karlsruhe, Germany). The magnetic characterizations were performed as follows: First, we measured the hysteresis (M-H) loops at room temperature by applying a magnetic field parallel and perpendicular to the metallic nuclei axis of the Ni2FeSi, Co2FeSi, and Co2MnSi MW samples to check the magnetic anisotropy and confirm the easy axis of the magnetization. Then, we checked the magnetic behavior of the samples in a wide range of temperature (5–400 K) by measuring the M-H loops parallel to the wire’s axis, i.e., the easy magnetization axis. Finally, we analyzed the thermal magnetization curves, i.e., the field cooling (FC) and field heating (FH) magnetizations curves at applied low external magnetic field, to check the irreversibility behavior or magnetic phase transition in the Ni2FeSi, Co2FeSi, and Co2MnSi MWs. All magnetization curves were measured using a PPMS (Physical Property Magnetic System, Quantum Design Inc., San Diego, CA, USA) vibrating-sample magnetometer.

3. Results

3.1. Chemical, Nominal Composition, and Microstructure Analysis

As mentioned in the previous section, the morphological and main geometrical parameters were evaluated using an optical microscope and SEM. Figure 1 illustrates the SEM images of the Ni2FeSi, Co2FeSi, and Co2MnSi MWs with fixed geometrical parameters. Table 1 shows the estimation of the metallic nucleus, dmetal, and the total diameters, Dtotal, of the Ni2FeSi, Co2FeSi, and Co2MnSi MWs. By calculating dmetal (µm) and Dtotal (µm), we can easily confirm that the samples have nearly the same geometrical parameters. The difference in the aspect ratios of all samples was around ± 0.1. We used EDX analysis to confirm the chemical compositions of the samples. As shown in Table 1, all the samples had the same stoichiometry 2:1:1. A higher amount of Si compared to Mn and Fe was observed in Ni2FeSi GCMWs, Co2FeSi MWs, and Co2MnSi MWs due to the additional signal of Si coming from the covering glass layer.
Figure 2 illustrates the microstructure investigation of Ni2FeSi, Co2FeSi, and Co2MnSi MWs measured by XRD at room temperature. The pattern starts from 2Ө = 23.8° to exclude the amorphous halo that comes from the covering glass layers. As shown in Figure 2, all the samples showed a crystalline structure with main peaks at 2Ө = 46.3°. Although the samples had the same geometrical parameters, changes in the microstructure were observed. The Ni2FeSi and Co2MnSi MWs shared two peaks at 2Ө = 68.6° and 2Ө = 85.1° with (400) and (420) reflections, respectively. Due to the absence of a (111) reflection in the Ni2FeSi MWs, the BCC single-phase microstructure with B2 type, i.e., (disordered) is supposed. Meanwhile, a well-defined FCC single phase with L21 ordered type was found for the Co2MnSi MWs. However, the two superlattice diffraction (111) and (200) peaks were significantly weaker compared to those for other elements belonging to the same period of the periodic table [48]. The intensities of these peaks may, therefore, be essentially undetectable if the majority or all the elements in the presented alloys belong to the same period in the elemental periodic table. For Co2FeSi MWs, the existence of two peaks only at 2Ө = 46.3° and 2Ө = 85.1°, corresponding with (220) and (420) reflections, fit very well with the FCC single phase with A2 type, i.e., disordered.
From detailed analysis of the XRD pattern of the Ni2FeSi, Co2FeSi, and Co2MnSi MW samples, we found that the lowest lattice parameters were detected for Co2FeSi MWs, where a = 2.81Å. The cell parameters for Ni2FeSi and Co2MnSi MWs were very similar, where a = 5.78 Å and 5.71 Å, respectively. However, although the samples had the same space group, i.e., Im3¯m (BCC) type, the crystallite size was different as illustrated in Table 2. The Co2FeSi and Co2MnSi glass-coated microwires had a roughly similar crystallite size (≈ 37 nm), while for Ni2FeSi MWs, it reduced to ≈ 21 nm. The values for crystallite size and the degree of microstructure order have a strong effect on the magnetic behavior of the samples. Thus, the diffraction peak at 2Ө = 46.3° for Ni2FeSi GCMWs appeared broader than those for the other samples.

3.2. Magnetic Characterization

3.2.1. Room-Temperature Magnetic Properties

To check the magnetic behavior of the Ni2FeSi, Co2FeSi, and Co2MnSi MWs at room temperature, we performed the magnetic measurements in two directions, axial, i.e., parallel to the metallic nuclei axis, and out-of-plane, i.e., perpendicular to the wire axis by using a PPMS magnetometer. The out-of-plane loops appeared linear with a vanishing coercivity and a reduced remanence, i.e., Hc and Mr ≈ zero (not shown). The vanishing out-of-plane Hc and Mr indicate that all the magnetization lies in the in-plane (axial) direction and the out-of-plane direction is the hard magnetization axis for all the MW samples.
Figure 3 shows the M-H loops of the Ni2FeSi, Co2FeSi, and Co2MnSi MWs at room temperature with an applied magnetic field parallel to the microwire axis, i.e., the axial direction. For Co2MnSi MWs, it appears that the easy magnetization axis is not perfectly axial and is possibly tilted at an angle, away from the wire axis. Unfortunately, we do not have a way to measure the angular magnetic behavior to accurately determine the magnetic anisotropy of the sample. Ni2FeSi MWs showed hard magnetic behavior with a coercivity of 138 Oe, which was 16 times higher than that of the Co2MnSi MWs and 3 times higher than that of the Co2FeSi MWs (see Table 3). The increase in the coercivity and the in-plane anisotropy field of Ni2FeSi MWs must be attributed to their different microstructure. Surprisingly, the smallest value for crystallite size was observed for the Ni2FeSi sample. Therefore, the high coercivity of the Ni2FeSi sample may be associated with its disordered microstructure of B2 type, which strongly affects the magnetization reversal process, the domain structure, and its movement. In addition, the magnetocrystalline anisotropy plays an important role in the overall magnetic behavior. Thus, the enhanced coercivity detected in Ni2FeSi MWs and the high reduced remanent magnetization of Co2FeSi MWs suggest a scenario in which the crystalline texture affects the magnetic anisotropy. In particular, the easy magnetization axis can be aligned along the (220) and (420) reflections. However, although the Co2MnSi MW sample showed a well-defined ordered structure with L21 type, the low reduced remanence and coercivity observed in the Co2MnSi MW sample can be due to the mismatching between the magnetocrystalline anisotropy and the crystalline structure. As demonstrated in our previous research, the magnetic anisotropy behavior of Heusler-based glass-coated microwires is primarily influenced by two main factors: uniaxial magnetic anisotropy and cubic magnetocrystalline anisotropy [14,17]. It has been reported elsewhere [18,19,20,21,30] that the ρ-ratio is directly related to the strength of internal stresses. Therefore, it is expected, that the ρ-ratio affects the relative content of the crystalline phase and correlates with modifications in the magnetic properties. Specifically, cubic magnetocrystalline anisotropy emerges as the predominant factor governing magnetic anisotropy. Regrettably, at present, experimental measurement of this type of anisotropy remains unfeasible. However, the presence of a roughly squared hysteresis loop strongly indicates its significant impact on the magnetic properties of the Ni2FeSi and Co2FeSi MW samples.

3.2.2. Temperature Dependence of Magnetic Properties

It is worth noting that the temperature stability of ferromagnetic materials is a crucial characteristic for their possible applications in spintronic and sensing devices. Hence, we investigated the magnetic behavior of the Ni2FeSi, Co2FeSi, and Co2MnSi MWs with a fixed ρ-ratio for a wide range of measurement temperatures, 5–400 K. The shape of the loops follows the same trend observed at room temperature: non-squared for the Co2MnSi MWs and quite squared for the Ni2FeSi and Co2FeSi MW samples. In Figure 4 and Figure 5, the M-H loops and the evolution of Hc and Mr with the temperature are shown. This behavior can be explained by considering that, for the Ni2FeSi and Co2FeSi MW samples, cubic magnetocrystalline anisotropy prevails up to 400 K.
By analyzing the M-H loops measured at the temperature range 5–350 K for Ni2FeSi, Co2FeSi, and Co2MnSi MWs with a fixed ρ-ratio, an interesting magnetic behavior was observed for the temperature dependence of Hc in Ni2FeSi MWs. First, the Ni2FeSi MWs showed the highest coercivity value at all temperature ranges compared to the Co2-based glass-coated samples with the same aspect ratio. In addition, the Hc temperature dependence did not show uniform behavior; two flipped points at T = 200 K and 50 K were observed. At these points, the tendency of Hc dramatically changed with temperature (see Figure 4a). Meanwhile, the temperature dependence of Hc for Co2FeSi and Co2MnSi MWs showed quite a stable tendency with temperature. The improved coercivity stability observed in Co2MnSi MWs is strongly related to the high-ordered microstructure with L21 type (see Figure 1). However, both the Ni2FeSi and the Co2FeSi MWs had a disordered microstructure with B2 type and A2 type, respectively. The Co2FeSi MWs showed higher coercivity thermal stability due to their A2 type microstructure, which shows higher energy stability compared to the B2 type [49,50,51]. Thus, the Co2FeSi MWs’ Hc vs. T appeared more stable compared to that of Ni2FeSi MWs. Additionally, the Mr vs. T tendency displayed regular ferromagnetic behavior with temperature, where a monotonic increase in Mr was observed with decreasing T (see Figure 4b). Both Ni2FeSi and Co2FeSi MWs had higher Mr values for the entire range of measuring temperatures compared to Co2MnSi MWs. The higher values of Mr for Ni2FeSi and Co2FeSi MWs suggest a dominant cubic magnetocrystalline anisotropy at a wide range of measuring temperatures.
Figure 6 shows the complete thermomagnetic behavior of Ni2FeSi, Co2FeSi, and Co2MnSi MWs with a fixed ρ-ratio. We studied the FC and FH temperature dependence of magnetization to check any possible phase transition. Thus, the measurements were performed at a low magnetic field of 50 Oe. The Ni2FeSi MWs showed regular ferromagnetic behavior wherein the FC and FH curves increased on decreasing the temperature from 400 to 5 K. For Co2FeSi and Co2MnSi MWs, the FC and FH magnetization curves showed non-homogonous behavior, besides an irreversible magnetic behavior that occurred at T = 125 K. Among the factors that affect irreversible behavior of the magnetization versus temperature are the induced martensitic transition and the change in the internal stresses associated with the glass-coating layer with temperature. As illustrated in Figure 6, the FC and FH magnetizations curves showed a perfect matching and monotonic increase on decreasing the temperature from 400 to 5 K in the Ni2FeSi sample (see Figure 6a). Accordingly, we can assume that the internal stress induced by the covering glass-layer during the fabrication process had a stable and uniform effect on the magnetic properties of the Ni2FeSi sample. Meanwhile, for Co2FeSi and Co2MnSi MWs, the internal stress did not show a uniform effect at all temperature ranges; from 400 to 300 K, the FC and FH had a good matching behavior, but on decreasing the temperature below 300 K, mismatching started to appear. Due to the disordered microstructure nature of the Co2FeSi MWs, the FC and FH did not have a smooth behavior with temperature unlike the Co2MnSi MWs.
The current results reveal that the influence of the internal stress induced by the glass coating layer is very sensitive to the chemical composition and the microstructure ordering of X2YZ-based glass-coated microwires. As a result, different magnetic and structural responses were observed in glass-coated microwires with different metallic nucleus chemical compositions. In our previous work, we illustrated how the internal stress is strongly related to the geometric dimensions and showed the importance of the external applied field, the annealing temperature/time condition, and the microstructure ordering of the host metallic alloys.

4. Discussion

During the preparation process of ferromagnetic glass-coated microwires, complex internal stresses of a tensor character are induced, determining their magnetic/structural properties. The difference between the thermal expansion coefficients of the metallic alloy and glass, quenching internal stresses associated with the fast solidification of the metallic alloy, and drawing stresses are the three main sources of internal stresses, σi, in glass-coated microwires [18,19,20,21,30]. It is generally accepted that the largest are the internal stresses arising due to the difference in the thermal expansion coefficients of the glass coating and the metallic alloy [18,19,20,21,30,43,44,45]. Moreover, all the internal stress components are affected by the geometrical parameter (ρ = dmetal/Dtotal). Thus, we can simply estimate σi as follows [24,45]:
σφ = σr = P = εEkΔ/(k/3 + 1)Δ + 4/3
σz = P(k + 1)Δ + 2/(kΔ + 1)
where σz, σφ, and σr are axial, circular, and radial stresses, respectively; Δ = (1 − ρ2)/ρ2; k =Eg/Em, Em, Eg—Young modulus of metallic nucleus and glass, respectively; ε = (αm − αg)(Tm − Troom), αm, αg are thermal expansion coefficients of metallic nucleus and glass, respectively, and Tm and Troom are the melting temperature and the room temperature, respectively. Therefore, a correlation is usually assumed between the magnitude of internal stresses and the geometric ratio ρ [45]. However, the metallic alloy composition is also relevant when using the Taylor–Ulitovsky method [24]. Thus, the alloy melting temperature, good wetting with glass, and the diffusion coefficients can substantially affect the microstructure and, hence, the magnetic properties of GCMWs [24]. The origin of the quenching internal stress is related to the solidification of the metallic alloy from the surface toward the wire axis [24,44]. Due to the different conditions for the solidification process for Co2FeSi, Co2MnSi, and Ni2FeSi GCMWs, the microstructure and even the magnitude of the quenching internal stress can be different. The same scenario is expected for the stresses induced by the difference in thermal expansion coefficients of the metallic alloy and glass and the drawing stresses, which are dependent on the metallic alloy as well. The previous investigations to evaluate such internal stress components took into consideration the successive concentric cylindrical shells solidifying consecutively, starting from the outside, due to the temperature gradient at the glass transition temperature [19,24,44,45].
The introduction of differences in ε, k, Tm, and Troom while keeping the geometrical parameters fixed is one of the routes to control the magnetic behavior of the different metallic nuclei of X2YZ-based glass-coated microwires.

5. Conclusions

In summary, we succeeded in preparing X2YZ-based glass-coated microwires with the same aspect ratio. In such X2YZ-based glass-coated microwires, we studied the effect of different chemical compositions of magnetic materials, i.e., metallic nuclei, on the internal stress. Also, we illustrated three main sources of the internal stresses that control the magneto-structural behavior of the X2YZ-based glass-coated microwires (thermal expansion coefficients of the metallic alloy and glass, quenching internal stresses, and drawing stresses). By fixing the internal stress, which mainly depends on the geometrical parameters, a notable variation in the magnetic and structural properties was observed. In the microstructure investigation, for Co2FeSi and Ni2FeSi MWs, the microstructure features were found to be disordered, varying between the A2 type and the B2 type, respectively. Meanwhile, a well-defined, ordered L21 type microstructure was observed for Co2MnSi-based glass-coated microwires. The variation in the microstructure has a strong effect on the magnetic behavior of the samples, resulting in a notable change in the Hc, Hk, Mr, FC, and FH tendency with temperature and magnetic field. There were also differences in the quenching internal stress and the internal stresses originated by different thermal expansion coefficients of the metallic alloy and glass, i.e., changing the metallic nucleus composition leads to changes in the magnetic and structural properties. The high thermal stability of coercivity observed in Co2MnSi- and Co2FeSi-based glass-coated microwires makes them promising candidates for different industrial applications.

Author Contributions

Conceptualization, M.S. and A.Z.; methodology, V.Z.; validation, M.S., V.Z. and A.Z.; formal analysis, M.S.; investigation, M.S. and A.Z.; resources, V.Z. and A.Z.; data curation, M.I.; writing—original draft preparation, M.S. and A.Z.; writing—review and editing, M.S. and A.Z.; visualization, M.S. and M.I.; supervision, V.Z. 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 the EU under the “INFINITE” (HORIZON-CL5-2021-D5-01-06) Horizon Europe project, and by the Government of the Basque Country, under the Elkartek (MINERVA, ZE-KONP and MAGAF) projects and under the scheme of “Ayuda a Grupos Consolidados” (Ref.: IT1670-22). M.S. wishes to acknowledge the funding within the Maria Zambrano contract by the Spanish Ministerio de Universidades and the 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.

Data Availability Statement

Not applicable.

Acknowledgments

The authors thank SGIker Magnetic Measurements Gipuzkoa (UPV/EHU/ ERDF, EU) for providing technical and human support.

Conflicts of Interest

The authors declare no conflict of interest.

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Crystals 13 01550 g001
Figure 1. SEM images of (a) Co2MnSi GCMWs, (b) Co2FeSi GCMWs, and Ni2FeSi GCMWs (c) illustrate the metallic nuclei, the coating layer, and the geometrical parameters.
Figure 1. SEM images of (a) Co2MnSi GCMWs, (b) Co2FeSi GCMWs, and Ni2FeSi GCMWs (c) illustrate the metallic nuclei, the coating layer, and the geometrical parameters.
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Figure 2. X-ray diffraction pattern of as-prepared Ni2FeSi (c), Co2FeSi (b), and Co2MnSi (a) glass-coated microwires at room temperature.
Figure 2. X-ray diffraction pattern of as-prepared Ni2FeSi (c), Co2FeSi (b), and Co2MnSi (a) glass-coated microwires at room temperature.
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Figure 3. Hysteresis loops at room temperature of as-prepared Ni2FeSi, Co2FeSi, and Co2MnSi glass-coated microwires with fixed geometric parameters.
Figure 3. Hysteresis loops at room temperature of as-prepared Ni2FeSi, Co2FeSi, and Co2MnSi glass-coated microwires with fixed geometric parameters.
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Figure 4. Hysteresis loops at different temperatures of as-prepared Ni2FeSi, Co2FeSi, and Co2MnSi glass-coated microwires with fixed aspect ratio. All loops were measured at a temperature range from 350 K to 5 K.
Figure 4. Hysteresis loops at different temperatures of as-prepared Ni2FeSi, Co2FeSi, and Co2MnSi glass-coated microwires with fixed aspect ratio. All loops were measured at a temperature range from 350 K to 5 K.
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Figure 5. Temperature dependence of the coercivity (a) and normalized remanence (b) of as-prepared Ni2FeSi, Co2FeSi, and Co2MnSi glass-coated microwires with fixed aspect ratio. (Lines for eye guide).
Figure 5. Temperature dependence of the coercivity (a) and normalized remanence (b) of as-prepared Ni2FeSi, Co2FeSi, and Co2MnSi glass-coated microwires with fixed aspect ratio. (Lines for eye guide).
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Figure 6. Temperature dependence of the measured magnetization of as-prepared (a) Ni2FeSi, (b) Co2FeSi, and (c) Co2MnSi glass-coated microwires with a fixed aspect ratio and an applied external magnetic field of 50 Oe.
Figure 6. Temperature dependence of the measured magnetization of as-prepared (a) Ni2FeSi, (b) Co2FeSi, and (c) Co2MnSi glass-coated microwires with a fixed aspect ratio and an applied external magnetic field of 50 Oe.
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Table 1. The geometrical parameters dmetal (µm), Dtotal (µm), nominal ratio, and average (Av.) of atomic percentage of Ni, Co, Fe, Mn, and Si elemental composition in as-prepared Ni2FeSi, Co2FeSi, and Co2MnSi glass-coated microwires.
Table 1. The geometrical parameters dmetal (µm), Dtotal (µm), nominal ratio, and average (Av.) of atomic percentage of Ni, Co, Fe, Mn, and Si elemental composition in as-prepared Ni2FeSi, Co2FeSi, and Co2MnSi glass-coated microwires.
Sampledmetal (µm)Dtotal (µm)Chemical CompositionNominal Ratio
Ni2FeSi10.79 ± 0.121.02 ± 0.1Ni51Fe23Si262:1:1
Co2FeSi10.35 ± 0.120.88 ± 0.1Co48Fe25Si312:1:1
Co2MnSi9.83 ± 0.119.94 ± 0.1Co46Mn24Si302:1:1
Table 2. Crystallographic information of as-prepared Ni2FeSi, Co2FeSi, and Co2MnSi glass-coated microwires with fixed aspect ratio.
Table 2. Crystallographic information of as-prepared Ni2FeSi, Co2FeSi, and Co2MnSi glass-coated microwires with fixed aspect ratio.
SampleCrystallite Size (nm)Space GroupCell Parameters
(a (Å))		Structural Designation
Ni2FeSi21.3 ± 0.3Fm3¯m (BCC)5.78B2 (disordered)
Co2FeSi37.3 ± 0.5Im3¯m (BCC)2.81A2 (disordered)
Co2MnSi36.92 ± 0.5Fm3¯m (FCC)5.71L21 (ordered)
Table 3. The coercivity (Hc), reduced remanence (Mr), and in-plane anisotropy field (Hk) of as-prepared Ni2FeSi, Co2FeSi, and Co2MnSi glass-coated microwires with a fixed aspect ratio measured at room temperature.
Table 3. The coercivity (Hc), reduced remanence (Mr), and in-plane anisotropy field (Hk) of as-prepared Ni2FeSi, Co2FeSi, and Co2MnSi glass-coated microwires with a fixed aspect ratio measured at room temperature.
SampleHc (Oe)MrHk (Oe)
Ni2FeSi138 ± 0.50.82 ± 0.01350 ± 0.5
Co2FeSi45 ± 0.50.92 ± 0.0188 ± 0.5
Co2MnSi7 ± 0.50.22 ± 0.0145 ± 2
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Salaheldeen, M.; Zhukova, V.; Ipatov, M.; Zhukov, A. Unveiling the Magnetic and Structural Properties of (X2YZ; X = Co and Ni, Y = Fe and Mn, and Z = Si) Full-Heusler Alloy Microwires with Fixed Geometrical Parameters. Crystals 2023, 13, 1550. https://doi.org/10.3390/cryst13111550

AMA Style

Salaheldeen M, Zhukova V, Ipatov M, Zhukov A. Unveiling the Magnetic and Structural Properties of (X2YZ; X = Co and Ni, Y = Fe and Mn, and Z = Si) Full-Heusler Alloy Microwires with Fixed Geometrical Parameters. Crystals. 2023; 13(11):1550. https://doi.org/10.3390/cryst13111550

Chicago/Turabian Style

Salaheldeen, Mohamed, Valentina Zhukova, Mihail Ipatov, and Arcady Zhukov. 2023. "Unveiling the Magnetic and Structural Properties of (X2YZ; X = Co and Ni, Y = Fe and Mn, and Z = Si) Full-Heusler Alloy Microwires with Fixed Geometrical Parameters" Crystals 13, no. 11: 1550. https://doi.org/10.3390/cryst13111550

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