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

We used the Taylor–Ulitovsky technique to prepare nanocrystalline Co2MnGe Heusler alloy glass-coated microwires with a metallic nucleus diameter of 18 ± 0.1 µm and a total diameter of 27.2 ± 0.1 µm. Magnetic and structural studies were carried out to determine the fundamental magneto-structural characteristics of Co2MnGe glass-coated microwires. XRD revealed a well-defined nanocrystalline structure with an average grain size of about 63 nm, lattice parameter a = 5.62 and a unique mixture of L21 and B2 phases. The hysteresis loops measured at different temperatures indicated a well-known ferromagnetic behavior for the reduced remanent, where a monotonic increasing in the reduced remanent and saturation magnetization occurs. The coercivity shows anomalous behavior compared to the Co2Mn-based glass-coated microwires. The magnetization curves for field cooling and field heating (FC–FH) demonstrate a considerable dependence on the applied magnetic field, ranging from 50 Oe to 20 kOe. Internal stresses, originated by the production process, resulted in various magnetic phases, which were responsible for the notable difference of FC and FH curves on magnetization dependence versus temperature. Furthermore, the ferromagnetic behavior and expected high Curie temperature, together with high degree of the L21 order, make it a promising candidate for many applications.This research was funded by the Spanish MICIN, under PID2022-141373NB-I00 project, by EU under “INFINITE” (Horizon Europe) project and by the Government of the Basque Country, under PUE_2021_1_0009 and Elkartek (MINERVA and ZE-KONP) projects and by under the scheme of “Ayuda a Grupos Consolidados” (Ref.: IT1670-22). In addition, MS wishes 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”)

Influence of the Geometrical Aspect Ratio on the Magneto-Structural Properties of Co2MnSi Microwires

This present study illustrates the strong effect of geometrical parameters on the magneto-structural properties of Co2MnSi glass-coated microwires prepared using the Taylor–Ulitovsky method. Thus, there are three samples with different geometrical aspect ratios (ρ). The XRD analysis shows a significant change by modifying the aspect ratio; for ρ = 0.42, the main peak with miller indices (220) is recognized as an A2-type disordered cubic structure. For the sample with ρ = 0.46, mixed L21 and B2 cubic structures are observed. Meanwhile, in the sample with a low aspect ratio, ρ = 0.30, the perfect L21 ordered cubic structure is attained. Magnetic characterization has been carried out at a wide range of temperatures and magnetic fields. A significant increase in coercivity and normalized reduced remanence by decreasing the aspect ratio is detected. The change in the magnetic properties is attributed to the modification in the microstructure, which is induced during the fabrication process. Such a dependence on the microstructure and magnetic properties on the ρ-ratio can be associated either with the internal stress distribution and magnitude or with different quenching rates of microwires with different aspect ratios. The current findings demonstrate the tunability of the microstructure and magnetic properties of Co2MnSi-glass-coated microwires simply via a small modification in the geometric properties during the manufacturing process and without excreting any additional post-processing. The variation in the geometric parameters of Co2MnSi glass-coated microwires allows us to tune the magnetic properties and structure, which is essentially advantageous for sensing device development.This research was funded by the Spanish MICIN, under PID2022-141373NBI00, by the EU under the “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). M.S. wishes 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, who not only provided limited funding but even expropriated 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

Carbon-Doped Co2MnSi Heusler Alloy Microwires with Improved Thermal Characteristics of Magnetization for Multifunctional Applications

In the current work, we illustrate the effect of adding a small amount of carbon to very common Co2MnSi Heusler alloy-based glass-coated microwires. A significant change in the magnetic and structure structural properties was observed for the new alloy Co2MnSiC compared to the Co2MnSi alloy. Magneto-structural investigations were performed to clarify the main physical parameters, i.e., structural and magnetic parameters, at a wide range of measuring temperatures. The XRD analysis illustrated the well-defined crystalline structure with average grain size (Dg = 29.16 nm) and a uniform cubic structure with A2 type compared to the mixed L21 and B2 cubic structures for Co2MnSi-based glass-coated microwires. The magnetic behavior was investigated at a temperature range of 5 to 300 K and under an applied external magnetic field (50 Oe to 20 kOe). The thermomagnetic behavior of Co2MnSiC glass-coated microwires shows a perfectly stable behavior for a temperature range from 300 K to 5 K. By studying the field cooling (FC) and field heating (FH) magnetization curves at a wide range of applied external magnetic fields, we detected a critical magnetic field (H = 1 kOe) where FC and FH curves have a stable magnetic behavior for the Co2MnSiC sample; such stability was not found in the Co2MnSi sample. We proposed a phenomenal expression to estimate the magnetization thermal stability, ΔM (%), of FC and FH magnetization curves, and the maximum value was detected at the critical magnetic field where ΔM (%) ≈ 98%. The promising magnetic stability of Co2MnSiC glass-coated microwires with temperature is due to the changing of the microstructure induced by the addition of carbon, as the A2-type structure shows a unique stability in response to variation in the temperature and the external magnetic field. In addition, a unique internal mechanical stress was induced during the fabrication process and played a role in controlling magnetic behavior with the temperature and external magnetic field. The obtained results make Co2MnSiC a promising candidate for magnetic sensing devices based on Heusler glass-coated microwires.This research was funded by the Spanish MICIN under PID2022-141373NB-I00, by EU under the “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 under the scheme of “Ayuda a Grupos Consolidados” (Ref.: IT1670-22). MS wishes 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

Ni-Mn-Sn-Cu Alloys after Thermal Cycling: Thermal and Magnetic Response

Heusler Ni-Mn-Sn-based alloys are good candidates for magnetic refrigeration. This application is based on cycling processes. In this work, thermal cycles (100) have been performed in three ribbons produced by melt-spinning to check the thermal stability and the magnetic response. After cycling, the temperatures were slowly shifted and the thermodynamic properties were reduced, the entropy changed at about 3–5%. Likewise, the thermomagnetic response remains similar. Thus, these candidates maintain enough thermal stability and magnetic response after cycling. Likewise, Cu addition shifts the structural transformation to higher temperatures, whereas the Curie temperature is always near 310 K. Regarding magnetic shape memory applications, the best candidate is the Ni49Mn36 Sn14Cu1 alloy.This study was funded by University of Girona PONT2020-01 and Spanish Mineco MAT2016-75967-P projects

Hydrogeochemical and Stable Isotope Data of the Groundwater of a Multi-Aquifer System in the Maknessy Basin (Mediterranean Area, Central Tunisia)

The Maknessy plain in central Tunisia is one of the most important agricultural basins in Tunisia. Given the semi-arid climate conditions, the irrigation of cultivated crops relies principally on the abstraction from groundwater resources. The assessment of the quality of the used water for agricultural purposes is crucial for safe production. Thus, the objective of this work is to assess the physicochemical quality of the irrigation water resources in this catchment area using a combined chemical, isotopic, and statistical approach. The waters analyzed are represented by two types of groundwater, mainly calcium hyper chloride and calcium sulfate. A multivariate statistical analysis (PCA and HCA) and a geochemical approach have been applied to study water quality as a function of chemical parameters, showing that the EC and TDS are the parameters influencing water quality. The stable isotopic compositions of the sampled waters range from -7.53 to -4.90% vs. VSMOW and from -53.6 to -32.2% vs. VSMOW for delta O-18 and delta H-2; they show the exchange between groundwater and rock and the evaporation effect. The isotopic data form three groups such as recent water, paleowater, and mixing water indicate the evaporation effect and interaction of the groundwater, and confirm that this aquifer has been recharged by current rainwater. So, these aquifers were recharged by precipitation derived from a mixture of cloud masses from the Atlantic Ocean and the Mediterranean Sea. The findings of this research are of important relevance for effective water resources management in this agro-based region. Indeed, the increased exploitation of these resources will induce a continuous reduction in the available resources and progressive degradation of the used water quality that may adversely impact the safe agricultural production and the economic resilience of the local population

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.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”)

Martensitic Transformation, Thermal Analysis and Magnetocaloric Properties of Ni-Mn-Sn-Pd Alloys

Martensitic transition and magnetic response of Ni50−x Pdx,y Mn36 Sn14−y (x = 0, 1, 2 and y = 0, 1) Heusler alloys were analysed. The crystalline structure of each composition was solved by X-ray diffraction pattern fitting. For x = 1 and 2, the L21 austenite structure is formed and, for y = 1, the crystallographic phase is a modulated martensitic structure. From differential scanning calorimetry scans, we determine characteristic transformation temperatures and the entropy/enthalpy changes. The temperatures of the structural transformation increase with the addition of Pd to replace Ni or Sn, whereas the austenitic Curie temperature remains almost unvarying. In addition, the magneto-structural transition, investigated by magnetic measurements, is adjusted by suitable Pd doping in the alloys. The peak value of the magnetic entropy changes reached 4.5 J/(kg K) for Ni50Mn36Sn13Pd1 (external field: 50 kOe).This research was funded by MINECO grant MAT2016-75967-P and UdG grant PONT2020/01

Elucidation of the Strong Effect of the Annealing and the Magnetic Field on the Magnetic Properties of Ni2-Based Heusler Microwires

We study the effect of annealing and the applied magnetic field from 50 Oe to 20 kOe on the magneto-structural behavior of Ni2FeSi-based Heusler microwires fabricated by using Taylor-Ulitovsky technique. Using the XRD analysis, a strong effect of annealing, manifested as the development of the crystallization process, was observed. The average grain size and crystalline phase content of annealed sample increase from 21.3 nm and 34% to 32.8 nm and 79%, respectively, as-compared to the as-prepared one. In addition, upon annealing, phase transforms into a monoclinic martensitic structure with a modulation of 10 M, which cannot be found in the as-prepared sample. Concerning the magnetic properties, both samples show ferromagnetic behavior below and above the room temperature, where the Curie temperature of Ni2FeSi is higher than the room temperature. The induced secondary phases have a noticeable effect on the magnetic behavior of the annealed sample, where a high normalized saturation magnetization (NMs) and low normalized reduced remenance (Mr = M/M5K), compared to the as-prepared have been detected. Additionally, the coercivity of annealed sample shows one flipping point at 155 K where its behavior changes with temperature. Meanwhile, the as-prepared sample show two flipped point at 205 K and 55 K. A mismatch between field cooling (FC) and field heating (FH) magnetization curves with temperature has been detected for annealed sample at low applied magnetic field. The difference in magnetic and structure behavior of Ni2FeSi microwires sample is discussed considering the effect of induced internal stresses by the presence of a glass coating and the recrystallization and stresses relaxation upon annealing.This research was funded by the Spanish MCIU, under PGC2018-099530-B-C31 (MCIU/AEI/FEDER, UE), by EU under “INFINITE”(Horizon 2020) project, by the Government of unding have been chethe Basque Country, under PUE_2021_1_0009 and Elkartek (MINERVA and ZE-KONP) projects and by under the scheme of “Ayuda a Grupos Consolidados” (Ref.: IT1670-22), by the University of Basque Country under the COLAB20/15 project and by the Diputación Foral de Gipuzkoa in the frame of Programa “Red guipuzcoana de Ciencia, Tecnología e Innovación 2021” under 2021-CIEN-000007-01 project. 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

Martensitic Transformation, Thermal Analysis and Magnetocaloric Properties of Ni-Mn-Sn-Pd Alloys

Martensitic transition and magnetic response of Ni50−x Pdx,y Mn36 Sn14−y (x = 0, 1, 2 and y = 0, 1) Heusler alloys were analysed. The crystalline structure of each composition was solved by X-ray diffraction pattern fitting. For x = 1 and 2, the L21 austenite structure is formed and, for y = 1, the crystallographic phase is a modulated martensitic structure. From differential scanning calorimetry scans, we determine characteristic transformation temperatures and the entropy/enthalpy changes. The temperatures of the structural transformation increase with the addition of Pd to replace Ni or Sn, whereas the austenitic Curie temperature remains almost unvarying. In addition, the magneto-structural transition, investigated by magnetic measurements, is adjusted by suitable Pd doping in the alloys. The peak value of the magnetic entropy changes reached 4.5 J/(kg K) for Ni50Mn36Sn13Pd1 (external field: 50 kOe)

Synthèse, caractérisation et étude magnétique des alliages à mémoire de forme de type Heusler Ni-Mn-Sn-X (X= Pd, Cu)

Cotutela Universitat de Girona i Université de SfaxShape memory alloys witch exhibit magnetically induced phase transformations at room temperatures are the most interesting for magnetic cooling applications. Heusler type alloys (both stoichiometric and non-stoichiometric) are among the most studied systems, as they permit the change of the transition temperatures due to compositional variations. The first Heusler alloys that have been studied in depth are Ni- Mn-Ga alloys. However, to overcome the high cost of Gallium and low martensitic transformation temperature, the search for Ga-free alloys has been recently endeavoured, principally, by introducing In, Sn or Sb. The purpose of this work is the production and characterization of non-stoichiometric Heusler alloys based on a Ni-Mn-Sn composition, with copper or Palladium doping. The effect of doping element will be determined, on the crystalline structure, the phase transition temperatures, the thermodynamic and magnetocaloric parameters. On the other hand, a heat treatment will be exerted on Ni-Mn-Sn-Cu alloys then characterize them in the same way. Shape memory alloys will be produced in the first step, by arc melting technique, to produce the bulk and then by melt spinning, to obtain shape memory ribbons. Produced samples are characterized by scanning electron microscopy (SEM) technique, to check the morphological structure of the alloys, microanalysis technique (EDX) to have the final composition experimentally, X-ray diffraction technique (XRD) to extract information from the crystal structure, differential scanning calorimetry (DSC) to study the thermal and thermodynamic variations induced by structural phase transformations and finally magnetometry techniques (Physical property measurement system, PPMS: VSM, resistivity, hysteresis cycles) to characterize the phase transformations behaviour and magnetocaloric effect under applied external magnetic fields. Among the results obtained in the present work it can be concluded that both Cu-doped and Pd-doped alloys have similar morphology. The reversible austenite-martensite transformation was detected in all ribbons. Cu or Pd doping tends to increase the structural transition temperatures. These changes in the magnetic and martensitic transformation temperatures are confirmed report directly to the ratio (e/a) of the alloy. Moreover, it’s emphasized the fact that Pd doped alloys show a good magnetocaloric effect (the maximum variation of ΔS is approximately 4.5 J / (Kg.K) for an applied magnetic field of 50 kOe and the refrigeration capacity is 28 J / kg). This dependence must allow the selection of the appropriate composition for the production of alloys with transformation into a desired temperature range. On the other hand, measurements of DRX, DSC and magnometry carried out on Ni-Mn-Sn-Cu alloys after application of thermal cycles of heating-cooling of 100 times, allowed us to certify the great stability of the alloys and the shape memory effect (minor change in phase transformation temperatures and curie temperatures)Els aliatges tipus Heusler (tant estequiomètrics com no estequiomètrics) es troben entre els sistemes més estudiats, ja que permeten el canvi de les temperatures de transició a causa de les variacions de la composició. Els primers aliatges de Heusler que s’han estudiat en profunditat són els aliatges de Ni-Mn-Ga. No obstant això, per superar l’elevat cost del gal i la baixa temperatura de transformació martensítica, recentment s’ha intentat buscar aliatges sense Ga, principalment, introduint In, Sn o Sb. L’objectiu d’aquest treball és la producció i caracterització d’aliatges de Heusler no estequiomètrics a partir d’una composició de Ni-Mn-Sn, amb dopatge de cobalt o pal·ladi. L'efecte de l'element dopant es determinarà, sobre l'estructura cristal·lina, les temperatures de transició de fase, els paràmetres termodinàmics i magnetocalòrics. D’altra banda, s’exercirà un tractament tèrmic sobre els aliatges de Ni-Mn-Sn-Cu per després caracteritzar-los de la mateixa manera. Els aliatges de memòria de forma es produiran en el primer pas, mitjançant la tècnica de la fusió de l’arc, per produir l’aliatge massiu i després per la fusió per obtenir cintes de memòria de forma. Les mostres produïdes es caracteritzen per la tècnica de microscòpia electrònica d’escombratge (SEM), per comprovar l’estructura morfològica dels aliatges, la tècnica de microanàlisi (EDX) per tenir la composició final de manera experimental, la tècnica de difracció de raigs X (XRD) per extreure informació de l’estructura cristal·lina, calorimetria d’escaneig diferencial (DSC) per estudiar les variacions tèrmiques i termodinàmiques induïdes per transformacions de fase estructurals i finalment tècniques de magnetometria (PPMS: VSM, resistivitat, cicles d’histèresi) per caracteritzar el comportament de les transformacions de fase i l’efecte magnetocalòric sota camps magnètics externs aplicats. Entre els resultats obtinguts en el present treball es pot concloure que tant els aliatges dopats amb Cu com els aliatges dopats amb Pd tenen una morfologia similar. La transformació reversible d'austenita-martensita es va detectar a totes les cintes. El dopatge Cu o Pd tendeix a augmentar les temperatures de transició estructural. Aquests canvis en les temperatures de transformació magnètica i martensítica es confirmen directament a la relació (e / a) de l'aliatge. A més, s’ha destacat el fet que els aliatges dopats amb Pd mostren un bon efecte magnetocalòric. Aquesta dependència ha de permetre seleccionar la composició adequada per a la producció d'aliatges amb transformació en un rang de temperatura desitjat. D’altra banda, les mesures de DRX, DSC i magnometria realitzades sobre aliatges Ni-Mn-Sn-Cu després de l’aplicació de cicles tèrmics de calefacció-refrigeració de 100 vegades, ens van permetre certificar la gran estabilitat dels aliatges i la efecte memòria de formaPrograma de Doctorat en Tecnologi