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.


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 promising candidates 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 & microdevices with improved processing and memory capability while consuming less power [10]. To address the various required criteria, such as high spin polarization or high the 1960s [37], is probably the most used fabrication method to make Heusler alloys glasscoated 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 non-expensive technique is that it allows the production of thin and long (up to several kilometers long) microwires with a wide diameter range (from 0.2 µm up to 100 µm) at a high rate (up to some 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]. Additional benefits of glass coating on microwires are better isolation and protection from the surroundings. Moreover, the fact that the glass coating is biocompatible, coupled with the commented properties, make this approach well-suited for biological applications [29,42,43]. Therefore, Heusler microwires of Co 2 FeSi are an interesting material for a broad range of applications and devices. As far as we know, there is no report up to date on the production and structural, mechanical, or magnetic properties of Co 2 FeSi-based glass-covered Heusler microwires with varied ρ-ratios, as well as the investigation of its influence on magneto-structure behavior.

Materials and Methods
Arc melting is a method of manufacturing Co 2 FeSi alloys that involves melting the precursor components together in an electric arc furnace. Typically, the following procedures are used to create Co 2 FeSi alloys by arc melting: (i) preparing the precursor ingredients. The precursor elements for the Co 2 FeSi alloy are weighed and deposited in a graphite crucible, containing cobalt (powder) (99.99%), iron (powder) (99.9%), and silicon (powder) (99.99%) supplied by Technoamorf S.R.L. Co. (Cisineu, Moldavia). (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 Co 2 FeSi alloy (ingot) is created as the ingredients consolidate. This process was then repeated five times to achieve perfect homogeneity and a homogeneous microstructure. Once the Co 2 FeSi alloy has solidified and formed an ingot, the ingot is used to prepare Co 2 FeSi 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 rather thin glass coatings, generally up to a few micrometers thick. This thin insulating coating 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. To summarize it, a glass capillary was filled with Co 2 FeSi alloy, molten using a high frequency inductor for heating an ingot over its melting temperature. The variation of the speed of wire drawing, alloy temperature, glass tube feed rate and of the rotation of the pick-up bobbin were the parameters used to control the diameter of the metallic nuclei, d metal (µm), and total diameter D total (µm) as explained in detail elsewhere [38]. Finally, the microwire is cooled with a coolant stream to complete the rapid melt quenching process. All geometric parameters of samples investigated in current study are listed in Table 1, also including a similar sample previously studied (in ref. [24]), whose results will be also discussed in the following section. 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 Co 2 FeSi glasscoated 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 in 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 the low magnetic field (H = 200 Oe). All magnetization curves were measured using a PPMS (Physical Property Magnetic System, Quantum Design Inc., San Diego, CA, USA) vibrating-sample magnetometer at temperatures, T, between 5 and 400 K for ZFC, FC, and FH magnetic curves. For the hysteresis 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/M 5K , where M 5K is the magnetic moment obtained at 5 K to avoid misleading of the estimation of the errors in the estimation of the magnetization saturation values.

Analysis of Chemical and Structural Data
The geometries (ρ-ratios) and chemical compositions of prepared samples are shown in Table 1. The variation of the microwires diameters (d metal and D total ) is achieved by controlling the drawing rate, alloy temperature, glass tube feed rate, and the receiving bobbin rotation speed [38]. Using the EDX data from Table 1, it was revealed that the metallic nucleus composition differed considerably from the stoichiometric one (Co 2 FeSi). The features of the preparation process, which involved alloy melting and drawing, were the cause of this slight variation. To quantify the difference, we checked the nominal composition for eight sites as illustrated in Figure 1a. An atomic average of Co 44 Fe 23 Si 33 was used to confirm that the true 2:1 ratio of Co and Fe was 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.  We used Scanning Electron Microscopy (SEM) and Energy Dispersive X-ra (JEOL-6610LV, JEOL Ltd., Tokyo, Japan) to determine the aspect ρ-ratio of Co2Fe coated microwires samples and its related nominal chemical composition.
The XRD structure analysis was carried on by using X-ray diffraction (XRD) B (D8 Advance, Bruker AXS GmbH, Karlsruhe, Germany).
The magnetic behavior was studied in two different ways: hysteresis loops peratures between 5 and 350 K, and thermomagnetic curves following three differ tocols, zero field cooling (ZFC), field cooling (FC), and field heating (FH) at the lo netic field (H = 200 Oe). All magnetization curves were measured using a PPMS (P Property Magnetic System, Quantum Design Inc., San Diego, CA, USA) vibrating magnetometer at temperatures, T, between 5 and 400 K for ZFC, FC, and FH m curves. For the hysteresis loops, we only focus on the in-plane configuration wh applied magnetic field is parallel to the wire axis. The results are provided in term normalized magnetization, M/M5K, where M5K is the magnetic moment obtained a avoid misleading of the estimation of the errors in the estimation of the magne saturation values.

Analysis of Chemical and Structural Data
The geometries (ρ-ratios) and chemical compositions of prepared samples are in Table 1. The variation of the microwires diameters (dmetal and Dtotal) is achieved trolling the drawing rate, alloy temperature, glass tube feed rate, and the receiving rotation speed [38]. Using the EDX data from Table 1, it was revealed that the nucleus composition differed considerably from the stoichiometric one (Co2FeSi). tures of the preparation process, which involved alloy melting and drawing, w cause of this slight variation. To quantify the difference, we checked the nominal sition for eight sites as illustrated in Figure 1a. An atomic average of Co44Fe23Si33 w to confirm that the true 2:1 ratio of Co and Fe was applied in all sites. A high Si ra found because of the interfacial layer that exists between the metallic nucleus and t covering.   In order to study the order state of our produced Co 2 FeSi 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 change in the geometric ρ-ratio has a strong influence on the structure of Co 2 FeSi 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 are detected. The wide halo at 2θ = 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 the metallic nucleus becomes evident with a notable peak at 2θ = 46.2 • , attributing to the (220) reflection. Further increase of geometric ρ-ratio results in the perfect crystalline structure of samples studied, where the crystalline peak intensity increases and an additional peak appears at 2θ = 85.4 • , corresponding to the (422) reflection. The analysis of XRD profiles of the two crystalline Co 2 FeSi samples, i.e., GCMW C (ρ = 0.30) and GCMW B (ρ = 0.43), indicates an A2 single-phase structure with a small tetragonal distortion (traces of tetragonal martensite phase), and a broadened peak around 22 • attributed to an amorphous state for GCMW C and mixed L2 1 or B2 phases with the amorphous state for GCMW B sample [34,35]. 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 change in the geometric ρ-ratio has a strong influence on the structure of Co2FeSi glass-coated microwires. For the sample with the lowest ρratio, i.e., ρ = 0.25, the sample shows an amorphous structure where no crystalline peaks are 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 the metallic nucleus becomes evident with a notable peak at 2Ө = 46.2°, attributing to the (220) reflection. Further increase of geometric ρ-ratio results in the perfect crystalline structure of samples studied, where the crystalline peak intensity increases and an 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 (ρ = 0.30) and GCMWB (ρ = 0.43), indicates an A2 single-phase structure with a small tetragonal distortion (traces of tetragonal martensite phase), and a broadened peak around 22 ⁰ attributed to an amorphous state for GCMWC and mixed L21 or B2 phases with the 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 leads to a small distortion of the crystalline structure [45]. The absence of a (400) peak around 85°, 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) Figure 2. XRD analysis of Co 2 FeSi glass-coated microwires with different aspect ratio measured at room temperature. The inset of Figure 2 indicates the A2-type cubic structure.
The (220) and (422) reflections in GCMW C 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 leads to a small distortion of the crystalline structure [45]. The absence of a (400) peak around 85 • , 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 L2 1 or B2 phases [48,49]. Nevertheless, the well-defined and sharp diffraction patterns in this sample (GCMW C sample) indicate a high crystallinity, as compared with the other two XRD spectra. As the development of traces of the secondary phase (tetragonal martensite) can affect magnetic behavior, this will be explored in more detail in the following sections.
We estimated the lattice parameters of the two crystalline Co 2 FeSi glass-coated microwires, and then we employed the Debye-Scherrer's equation, as presented in our previous work [23], to investigate the microstructure of Co 2 FeSi in greater depth. Using this methodology, we can estimate the average grain size, D g , associated with the principal peaks, which is approximately 17.8 m, 37.6 nm, and 45.8 nm for GCMW**, GCMW B , and GCMW C of Co 2 FeSi microwires, respectively, as illustrated in Table 2. Thus, D g has a monotonic increase with increasing the aspect ratio.  Figure 3 shows the magnetic hysteresis loops of Co 2 FeSi-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 Co 2 FeSi alloy greater than 1100 K [46]. The sample with a low ρ-ratio exhibits soft magnetic properties with coercivity, H c , around 14 Oe, and a non-square hysteresis loop shape (Figure 3a). However, the sample with the largest ρ-ratio shows almost perfectly square hysteresis loops with higher H c (about 87 Oe), than Co 2 FeSi with a low ρ-ratio (see Figure 3b,c). In addition, the hysteresis loop shows multistep magnetic behavior (indicated with arrows in Figure 3c). The almost square hysteresis loops for the GCMW C microwire with normalized remanent, M r , near 0.96 indicates the axial character of magnetic anisotropy with the easy axis of magnetization along the direction of the applied magnetic field. Thus, the increase in ρ-ratio affects the magnetocrystalline anisotropy, and its direction has the same direction of (220) and (420), as illustrated in the structural section. However, in the sample GCMW B with a crystalline structure, non-perfectly square loops are observed. Such change in the hysteresis loop shape must be related to the presence of a considerable amount of amorphous phase beside the disordered B2 or little-ordered L2 1 structures. In our previous work at the same alloys, but with a low ρ-ratio (ρ = 0.26), the enhancement of the magnetocrystalline anisotropy, the squareness, and coercivity of Co 2 FeSi glass-coated microwires after annealing was observed [21,22,24]. As we illustrated in our previous work, the two main factors affecting the magnetic anisotropy behavior in Heusler-based glass-coated microwires are uniaxial magnetic anisotropy and cubic magnetocrystalline anisotropy [21,22,24]. By increasing the ρ-ratio, an enhancement in the crystalline phase content correlates with the magnetic property modification, i.e., the main factor controlling the magnetic anisotropy is the cubic magnetocrystalline anisotropy. Unfortunately, currently, we are not able to measure this type of anisotropy experimentally, but the perfectly square loop indicates its strong effect on the GCMW B and GCMW C samples. As seen in Figure 4, the GCMWc sample shows the highest anisotropy field H k , coercivity H c , and normalized remnant M r . The odd behavior of H k is likely related to the big amorphous phase present in GCMW A and GCMW B samples, as the behavior of Hc for these two samples is also quite similar (there is not a decrease, as in the case of the H k , but the values are almost the same) and maybe the growth of the crystalline structure eases initially the reduction of the anisotropy field. In addition, the different types of microstructures (L21, B2, and A2) can also strongly affect the H k behavior. field Hk, coercivity Hc, and normalized remnant Mr. The odd behavior of Hk is likely related to the big amorphous phase present in GCMWA and GCMWB samples, as the behavior of Hc for these two samples is also quite similar (there is not a decrease, as in the case of the Hk, but the values are almost the same) and maybe the growth of the crystalline structure eases initially the reduction of the anisotropy field. In addition, the different types of microstructures (L21, B2, and A2) can also strongly affect the Hk behavior.

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 Co 2 FeSi glass-coated microwires with different ρ-ratios. The shape of the loops follows the same trend observed at room temperature: non-square for the GCMW A sample, quite square for the GCMW B one, and almost square for the GCMW C one (loops not shown). In Figure 5, the evolution of H c and M r with the temperature is shown. This behavior demonstrates that for the GCMW C sample, cubic magnetocrystalline anisotropy prevails up to 350 K.
havior 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 six times higher than those of the GCMW**, GCMWA and GCMWB samples. GCMW**, GCMWA, and GCMWB samples show quite similar values of the Hc where the difference between the average value of coercivity is about 2 Oe. By estimating the differences in 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, GCMW**, GCMWB, and GCMWC samples, show higher temperature stability than the amorphous GCMWA sample. Hence, the ΔHc is 11 Oe, 3.5, and 9 Oe for GCMW**, GCMWB, and GCMWC samples, respectively, whereas ΔHc is 15 Oe for the GCMWA one. The magnetic stability is clearer in the case of Mr tendency with the 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, respectively (see Table 3). Meanwhile, the behavior of Mr of GCMWA is rather different, compared to the other samples with higher ρ-ratios, where a monotonic increase with decreasing the temperature has been observed. By analyzing the hystersis loops measured at temperature range, 5-350 K of Co 2 FeSi glass-coated microwires with different ρ-ratio, an interesting magnetic behavior is found for both the temperature dependence of H c and of the normalized remanence, M r . GCMW C sample shows the highest value of the coercivity at the all measuring range of temperature range, with an average value of H c six times higher than those of the GCMW**, GCMW A and GCMW B samples. GCMW**, GCMW A , and GCMW B samples show quite similar values of the H c where the difference between the average value of coercivity is about 2 Oe. By estimating the differences in the coercivity (∆Hc) between the maximum value of coercivity (H c (max) ) and the lowest value of the coercivity (H c (min) ) for all samples, we pretend to show its stability with temperature. The samples with a clear crystalline phase, GCMW**, GCMW B, and GCMW C samples, show higher temperature stability than the amorphous GCMW A sample. Hence, the ∆Hc is 11 Oe, 3.5, and 9 Oe for GCMW**, GCMW B, and GCMW C samples, respectively, whereas ∆Hc is 15 Oe for the GCMW A one. The magnetic stability is clearer in the case of Mr tendency with the temperature of Co 2 FeSi glass-coated microwires with different ρ-ratios. As shown in Figure 5b, both GCMW B and GCMW C samples show high stability with temperature, with ∆M r 0.05 and 0.06, respectively (see Table 3). Meanwhile, the behavior of Mr of GCMW A is rather different, compared to the other samples with higher ρ-ratios, where a monotonic increase with decreasing the temperature has been observed. Table 3. The geometrical parameters and average (Av.) of Co 2 FeSi glass-coated microwires with different aspect ratios.

∆H c (H c (max) − H c (min) ) ∆M r (M r (max) − M r (min) )
GCMW A 15 ± 2 Oe 0.7 ± 0.1 GCMW** 11 ± 1 Oe 0.6 ± 0.1 GCMW B 3.5 ± 0.5 Oe 0.06 ± 0.01 GCMW C 9 ± 2 Oe 0.05 ± 0.01 GCMW**: Co 2 FeSi glass-coated microwires with (ρ = 0.25) [24]. Figure 6 shows the complete thermomagnetic behavior of Co 2 FeSi 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 a low magnetic field of 200 Oe. For the GCMW A sample, the ZFC, FC, and FH magnetizations curves show non-homogonous behavior, besides an irreversible magnetic behavior at T = 150 K. Such irreversibility has been observed in our previous work deal-ing with Co 2 FeSi-based glass-coated microwires with aspect ratio ρ = 0.25, i.e., GCMW**, (see [21,22,24]). In this work, we have illustrated that the irreversibility is enhanced by performing annealing at 873 K and 973 K for 1 h. The induced martensitic transition and the change 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, such as the Co2FeSi glass-coated microwires with ρ = 0.25, i.e., GCMW** [21,22,24]. For the GCMW A sample, which is totally in an amorphous state (see Figure 2), the main reason for the irreversibility behavior is the strong internal stress induced by the glass covering layer. For GCMW B and GCMW C samples, with 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 L2 1 cubic structure for GCMW C and GCMW B , respectively.
We believe that increasing the ρ-ratio of Co 2 FeSi glass-coating microwires affects recrystallization, atomic ordering, and stress reduction. Furthermore, for samples with a high ρ-ratio, the induced L2 1 /B2 and A2 cubic structure types generate a strong magneto crystalline anisotropy, explaining the behavior of magnetic properties such as H c , M r , H k , and thermomagnetic curves with temperature. In fact, as shown in several previous publication, the internal stress values are affected by the ρ-ratio: the lower the ρ-ratio, the higher the internal stresses related to the presence of the glasscoating [50][51][52]. On the other hand, the glass-coating thermal conductivity can affect the quenching rate of the metallic nucleus: a lower quenching rate must be at the origin of higher crystallinity of the microwires with relatively thick glass-coating [27]. The aforementioned internal stresses together with the samples' microstructure (average grain size) can affect the hysteresis loops. Additionally, the presence of the interfacial layer between the metallic nucleus and glass-coating, reported by us earlier can affect the saturation magnetization [53]. Such influence of the interfacial layer must be more appreciable for the thinner d metal -values.
In summary, Co 2 FeSi glass-coated microwires are an excellent candidate for a wide range of industrial applications, especially for sensors, due to their perfect squared loops at a wide temperature range and homogenous thermomagnetic behavior with temperature.

Conclusions
In summary, we have fabricated Co 2 FeSi-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 Co 2 FeSi 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 Co 2 FeSi glass-coated microwires and makes it a suitable candidate for magnetic sensing.  . 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.

Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.