Search Results (191)

This study presents a comparative investigation of MgCu intermetallic compounds, CuCoMnSn Heusler alloys, and carbon steel for spur gear applications using a novel tooth contact analysis (TCA) method. The TCA employs a nonlinear two-variable equation, providing a fast and accurate computational tool for evaluating gear contact behavior. By integrating material-specific elastic properties from density functional theory (DFT) studies, the analysis predicts contact paths, stress distributions, and responses to angular misalignments. Material selection strongly influences gear performance: MgCu is promising for lightweight applications, while CuCoMnSn is better suited where mechanical performance is prioritized. The CuCoMnSn alloy also exhibits half-metallic ferromagnetic behavior, offering potential functional advantages beyond mechanical performance. These results highlight the promise of intermetallics and Heusler alloys for high-performance, misalignment-tolerant gears and demonstrate the effectiveness of combining DFT-informed material modeling with the novel TCA method for optimized spur gear design. Full article

Employing ab initio electronic structure methods, in this study, I examine the effect of order on the spin gapless semiconducting behavior of the Mn₂CoAl Heusler compound. The occurrence of atomic disorder in general destroys the spin gapless semiconductivity observed in the inverse XA lattice structure; however, in some cases, novel magnetic configurations emerge. In the case of structures derived from the XA structure, where only Mn-Co or Mn-Al atoms are mixed, Mn₂CoAl alloy presents a half-metallic magnetic character. In the case of full disorder (A2 lattice structure), where atoms occupy all sites with the same probability, the ground state is an antiferromagnetic metallic one. The L2₁ and B2 lattice structures, where Mn atoms occupy both sites of a similar local environment, correspond to a ferromagnetic state of very high spin magnetic moment per formula unit. The present study encompasses a much larger variety of disordered structures in comparison with other studies in the literature. It concludes that the control and minimization of the concentration of impurities at anti-sites is imperative to achieving optimal performance in spintronic devices based on spin gapless semiconducting Mn₂CoAl. Full article

As a new full Heusler compound, the Cr₂ZrP alloy has attracted significant attention due to its potential applications in spintronics. In this paper, the electronic, magnetic, and mechanical properties of the Cr₂ZrP alloy were systematically studied using first-principles calculations. The results show that the alloy is a half-metallic ferromagnet with high stability: it exhibits majority-spin-channel semiconductor behavior and minority-spin-channel metallic behavior at the Fermi level, with 100% spin polarization. The total magnetic moment is 3.00 μB, which is consistent with the Slater-Pauling behavior of half-metallic ferromagnets. When the lattice parameter changes by ±5%, the total magnetic moment and 100% spin polarization remain robust, demonstrating excellent mechanical magnetic coupling stability. The mechanical property analysis further revealed that Cr₂ZrP meets the mechanical stability criterion of the cubic system and has a high bulk modulus (~172.8 GPa) and a high Debye temperature (~377 K). At the same time, its Pugh ratio (B/G ≈ 2.96) and Poisson ratio (ν ≈ 0.35) showed that the material had good ductility. The three-dimensional surface plot of Young’s modulus confirmed the obvious anisotropy of mechanical properties. This study theoretically confirmed that the Cr₂ZrP alloy exhibits ideal half-metallic properties, robust magnetic order, good mechanical stability, and ductility, making it a promising candidate for future spintronic devices. Full article

The present study investigated the magnetic hysteresis properties (coercivity and remanent magnetization) of the Zr₂RhTl Heusler alloy using effective field theory (EFT). The study found that the coercive field of Zr₂RhTl reaches a maximum at a specific critical temperature, T_ch, at which the hardness of magnetic materials increases with the coercive field. This behavior is called the “critical hardness temperature (T_ch)”. The hardness of the Zr₂RhTl Heusler alloy increases with temperature until T_ch, reaching a maximum at T_ch. In contrast, it exhibits soft magnetic behavior at T < T_ch and T > T_ch. We suggest that this maximum hardness behavior can enable a new class of thermo-hardness sensors (THSs) and actuators (THAs). Full article

We studied the changes of martensite average temperature T_M in a wide range of Heusler alloys derived from a Ni-Mn-Ga multifunctional compound prepared by arc melting. Based on prepared alloys and supplemented by the literature data, we demonstrated that criteria based on valence electron or non-bonding electron concentration per atom often failed in many different cases, in particular for isoelectronic compounds and Heusler alloys with Sb and Sn. Thus, we suggest an empirical criterion for estimating the temperature of martensitic transformation T_M in Ni-Mn-based Heusler alloys. It is built on valence electron concentration per atomic volume. Suggested criterion well-describes the experiment and data available in literature. Although it can be used for predicting T_M in complexly alloyed Ni-Mn-based Heusler alloys. Full article

A Ni₂MnSn Heusler alloy composition of elemental powders was high-energy milled for a short time for powder activation. The milling times were chosen to be 1 and 4 h to study how mechanical mixing triggers the phase formation in the Ni-Mn-Sn system. After milling, the samples were analyzed by differential scanning calorimetry and the thermal events of Ni₂MnSn L₂₁ phase formation were investigated. The milled samples were compacted at 700 MPa and annealed in a vacuum for 10 min at different temperatures (230 °C, 330 °C, and 600 °C). The annealing temperatures were chosen to emphasize the activated powders’ behavior before and after Sn melting on L₂₁ Structure formation. Using X-ray diffraction and Rietveld analysis, the phase quantity was computed, showing that the largest L₂₁ phase (63%) can be obtained from the elemental powder mixture due to Sn melting during the annealing. For milled samples, a Ni₃Sn₄ phase was obtained by milling, and by annealing this phase, along with the remaining element, it reacts to form a Ni₂MnSn L₂₁ phase and a Ni₃Sn₂ phase. The microstructural evolution of the phase was illustrated by backscattering electron microscopy for milled and subsequent annealed samples, and, by image analysis, a correlation of the phase’s amount was performed. The results of the image analysis were correlated with the X-ray diffraction patterns. Full article

The first-principles method using density functional theory (DFT) reveals the mechanics, electronic structure, and magnetic properties of six Zr-based equiatomic quaternary Heusler compounds and their transformation under hydrostatic pressure. The results show that these compounds maintain mechanical stability under hydrostatic pressures of 0–100 GPa, and the ductility of all the alloys is improved except ZrCrFeGe. In the ground state structure, ZrVFeAl and ZrCrFeGe are half metals, ZrVCoAl and ZrCrFeAl are spin gapless semiconductors, while ZrCrMnAl and ZrMnFeAl are regarded as nearly half metals. ZrVFeAl, ZrVCoAl, ZrCrFeAl, and ZrCrFeGe have high spin polarization and satisfy the Slater–Pauling rule, and their spin-flip band gaps are 0.43 eV, 0.35 eV, 0.14 eV, and 0.11 eV, respectively. These half-metallic compounds maintain half-metallicity within a certain pressure range, while spin gapless semiconductors (SGS) complete the SGS~half-metal~near-half-metal transition under hydrostatic pressure. These half-metallic compounds and spin gapless semiconductors are ideal candidates for spintronic applications. Full article

Intermetallic NiMn-based Heusler alloys (HAs) have garnered considerable attention due to their multifunctionality and applications in various fields, including sensors, actuation, refrigeration, and waste heat harvesters. Among the NiMn-based alloys, Ni-Mn-Sn alloys have gained considerable attention since their structural and magnetic transformations were discovered. Many studies have been conducted with various compositions and shapes to investigate the physical properties of Ni-Mn-Sn alloys, which offer several advantages, including non-toxicity, low cost, and abundant constituents. The Co-doping effect on the physical properties of Ni-Mn-Sn alloys has been widely reported. This doping can rectify the ternary Ni-Mn-Sn Heusler compound’s brittleness by crystallizing a disordered face-centered cubic (fcc) γ-phase. In this study, a polycrystalline Ni₄₂Mn₄₆CoSn₁₁ Heusler alloy was prepared by high-frequency fusion (HF), using a Lin Therm 600 device, from pure Ni, Mn, Sn, and Co elements with appropriate proportions. X-ray diffraction, scanning electron microscopy, and magnetic magnetometry devices were used to study the structural, microstructural, and magnetic properties. The XRD results revealed the coexistence of a disordered 7 M martensite phase (~88%) and a disordered cubic solid solution γ-phase (~12%). The alloy underwent a second-order ferromagnetic-to-paramagnetic phase transition at a Curie temperature of 350 K. Landau and Hamad’s theoretical models were used to plot the magnetic entropy change. The magnetocaloric properties (the maximum entropy change value, ΔS_M, the full width at half maximum of the entropy change curve, δT_FWHM, the relative cooling power, RCP, and the heat capacity, ΔC_P,H) were calculated using isothermal magnetization curves with the phenomenological model of Hamad. Full article

Heusler-type metamagnetic shape memory alloys (MMSMAs) exhibit a large functional response associated with a first-order martensitic transformation (MT). The strong magneto-structural coupling combined with the presence of mixed magnetic interactions enables controlling this MT by means of a magnetic field, resulting in different multifunctional properties, among them giant magnetoresistance, metamagnetic shape memory effect (MMSM), or inverse magnetocaloric effect (MCE). Not only the shift rate of MT as a function of the magnetic field but also its eventual suppression are key parameters in order to develop these effects. Here we present our findings concerning a detailed study of the magnetic field-induced MT and its suppression in MnNi(Fe)Sn MMSMAs, by applying strong steady magnetic fields up to 33 T. These measurements will lead to the creation of the T-μ₀H phase diagrams of the MT. Moreover, we will also give light to the effect of Fe—content and, as a direct consequence, the magnetic coupling on the suppression of the magnetostructural transformation. Full article

Over the last century, improvements in computational power resulting from the exponential growth of microelectronics have been the driving force of outstanding global economic growth as well as of deep changes in society and ethical values. Manufacturing of silicon-based memory cells has, as a matter of fact, become an industry of strategic importance also from a geopolitical perspective. Despite such advancements, a lot of concern has recently aroused as physical limitations such as tunnel-effect phenomena, current leakage, and high power consumption are increasingly hindering further improvements in dynamic random-access memory. Spintronic technologies are promising alternatives to overcome such issues, being considered no longer merely an academic subject of interest, but increasingly becoming an industrial reality. In this review work, the history and the physical principles of spintronic devices are presented, focussing on new, groundbreaking materials. Concepts are exposed step by step and in an easy-to-understand manner, allowing even researchers who are not specialized in the fields of spintronics, microelectronics, and hardware engineering to understand the fundamentals and gain initial insight into the topic. Special attention is paid to half-metallic ferromagnets and Heusler alloys, which are considered among the most promising materials for the future of spintronics. Full article

The crystal structure, texture, martensitic transformation, and magnetic properties of magnetic shape-memory Heusler alloys of Ni_51−xMn_33.4In_15.6V_x (x = 0; 0.1; 0.3; 0.5; 1) were investigated. Experimental studies of the magnetic properties and meta-magnetostructural transition (martensitic transition—MT) confirm the main sensitivity of the martensitic transition temperature to vanadium doping and to an applied magnetic field. This makes this family of shape-memory alloys promising for use in numerous applications, such as magnetocaloric cooling and MEMS technology. Diffuse electron scattering was analyzed, and the structures of the austenite and martensite were determined, including the use of TEM in situ experiments during heating and cooling for an alloy with a 0.3 at.% concentration of V. In the austenitic state, the alloys are characterized by a high-temperature-ordered phase of the L2₁ type. The images show nanodomain structures in the form of tweed contrast and contrast from antiphase domains and antiphase boundaries. The alloy microstructure in the temperature range from the martensitic finish to 113 K consists of a six-layer modulated martensite, with 10 M and 14 M modulation observed in local zones. The morphology of the double structure of the modulated martensite structure inherits the morphology of the nanodomain structure in the parent phase. This suggests that it is possible to control the structure of the high-temperature austenite phase and the temperature of the martensitic transition by alloying and/or rapidly quenching from the high-temperature phase. In addition, attention is paid to maintaining fine interface structures. High-resolution transmission electron microscopy showed good coherence along the austenite–martensite boundary. Full article

This study investigates the electronic, magnetic, and transport properties of the Co_0.5Mn_1.5Al half-Heusler alloy, a promising candidate for spintronic applications due to its potential half-metallic and ferrimagnetic characteristics. Experimental efforts focus on structural characterization using X-ray diffraction to examine substitutional disorder, such as Co/Mn site migration and Mn/Al site mixing, and their impacts on magnetic and transport properties. Magnetic characterization, including magnetization and susceptibility, reveals an N-type ferrimagnetic behaviour with a Curie temperature of 670 K. Transport experiments probe resistance and magnetoresistance across various temperatures and magnetic fields to uncover conduction mechanisms and spin-dependent effects. Theoretical band structure calculations, utilizing the Korringa–Kohn–Rostoker Green’s function method, investigate the electronic structure and the role of disorder in shaping magnetic and transport properties. This integrated experimental and theoretical approach aims to clarify the alloy’s suitability for applications in exchange bias or antiferromagnetic spintronics. Full article

The nanostructural features of a mechanically alloyed Sb-doped (Ti_0.4Zr_0.6)_0.7Hf_0.3NiSn thermoelectric (TE) Half-Heusler (HH) compound were addressed using Transmission Electron Microscopy (TEM) coupled with Energy Dispersive Spectroscopy measurements and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The EXAFS measurements at the Ni-K, Sn-K, Zr-K, and Hf-L₃-edge were implemented in an effort to reveal the influence of Hf and Zr incorporation into the crystal with respect to their previously measured TE properties. The substitution of Ti by Hf and Zr is expected to yield local lattice distortions due to the different atomic sizes of the dopants or/and electronic charge redistribution amongst the cations. However, the material is characterised by a high degree of crystallinity in both the short and long-range order, on average, and the nominal stoichiometry is identified as (Zr_0.42Hf_0.30Ti_0.28)NiSn_0.98Sb_0.02. The synergistic effect of minimization of extended structural defects or lattice distortions and considerable alloying-induced point defect population contributes to the improved TE properties and leads to the previously reported enhancement of the figure of merit of the mixed HHs. Full article

This review article provides an in-depth analysis of recent advancements in the fabrication, structural characterization, and magnetic properties of Heusler alloy glass-coated microwires, focusing on Co₂FeSi alloys. These microwires exhibit unique thermal stability, high Curie temperatures, and tunable magnetic properties, making them suitable for a wide range of applications in spintronics, magnetic sensing, and biomedical engineering. The review emphasizes the influence of geometric parameters, annealing conditions, and compositional variations on the microstructure and magnetic behavior of these materials. Detailed discussions on the Taylor–Ulitovsky fabrication technique, X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) provide insights into the structural properties of the microwires. The magnetic properties, including room-temperature behavior, temperature dependence, and the effects of annealing, are thoroughly examined. The potential applications of these microwires in advanced spintronic devices, magnetic sensors, and biomedical technologies are explored. The review concludes with future research directions, highlighting the potential for further advancements in the field of Heusler alloy microwires. Full article

We studied the influence of annealing on the magnetic properties and microstructure of ultrathin (metallic nucleus diameter ≈ 5 μm, total diameter ≈ 19 μm) Heusler-type NiMnGa glass-coated microwires prepared using the Taylor–Ulitovsky method. The as-prepared NiMnGa microwires exhibit unexpectedly strong magnetic anisotropy, characterized by a coercivity exceeding 3 kOe at room temperature. Furthermore, their Curie temperature (T_c) lies above room temperature. Additionally, a spontaneous exchange bias of approximately 120 Oe is observed in the as-prepared sample at 100 K. Annealing the microwires leads to a decrease in coercivity, spontaneous exchange bias, and T_c values. Notably, the annealing process shifts the T_c of the samples closer to room temperature, making them more suitable for magnetic solid-state refrigeration applications. Moreover, the hysteresis observed in the temperature dependence of magnetization for the samples annealed for 1 h and 2 h, along with the magnetic softening observed at around 260 K, is attributed to a first-order phase transformation. The observed changes are discussed in the context of internal stress relaxation after annealing, the nanocrystalline structure of both the as-prepared and annealed samples, the recrystallization process, and the magnetic ordering of phases identified in the as-prepared sample and those appearing during recrystallization. The glass coating on microwires offers benefits like better flexibility and resistance to damage and corrosion. However, it is important to recognize that this coating can substantially alter the microwires’ magnetic characteristics. Consequently, precise control over the annealing process is vital to obtain the specific martensitic transformation needed. Full article