Search Results (10)

The full Heusler alloys Ni₂MnZ (Z = In, Sn, Sb) exhibit ferromagnetic properties with a Curie temperature (T_C) above room temperature. The magnetic properties of Ni₂MnZ (Z = In, Sn, Sb) were studied through a combination of experiments and band calculations under ambient and elevated pressures. The main results of this study open up further prospects for controlling the magnetic properties of the multifunctional Heusler alloys Ni₂Mn_1+xZ_1−x (Z = In, Sn, Sb) and their practical application. Full article

Manganese-based alloys with the composition Mn₂FeZ (Z = Si, Al) have been extensively investigated in recent years due to their potential applications in spintronics. The Mn₂FeSi alloy, prepared in the form of ingots, powders, or ribbons, exhibits either a cubic full-Heusler (L2₁) structure, an inverse-Heusler (XA) structure, or a combination of both. In contrast, the Mn₂FeAl alloy has so far been synthesized only in the form of ingots, featuring a primitive cubic (β-Mn type) structure. This study focuses on the new quaternary Mn₂FeSi_0.5Al_0.5 alloy synthesized from pure Mn, Fe, Si, and Al powders via mechanical alloying. The elemental powders were ball-milled for 168 h with a ball-to-powder ratio of 10:1, followed by annealing at 550 °C, 700 °C, and 950 °C for 8 h in an argon protective atmosphere. The results demonstrate that annealing at lower temperatures (550 °C) led to the formation of a Heusler structure with a lattice constant of 0.5739 nm. Annealing at 700 °C resulted in the coexistence of several phases, including the Heusler phase and a newly developed primitive cubic β-Mn structure. Further increasing the annealing temperature to 950 °C completely suppressed the Heusler phase, with the β-Mn structure, having a lattice constant of 0.6281 nm, becoming the dominant phase. These findings confirm the possibility of tuning the structure of Mn₂FeSi_0.5Al_0.5 alloy powder—and thereby its physical properties—by varying the annealing temperature. The sensitivity of magnetic properties to structural changes is demonstrated through magnetization curves and zero-field-cooled/field-cooled curves in the temperature range of 5 K to 300 K. Full article

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 (H_c) compared to Co₂FeSi and Co₂MnSi MWs. The H_c 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 (H_c and M_r) of X₂YZ MWs, we deduced that the H_c showed a stable tendency for Co₂MnSi and Co₂FeSi MWs. Meanwhile, two flipped points were observed for Ni₂FeSi MWs, where the behavior of H_c changed with temperature. For M_r, 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. Full article

In this theoretical study, we investigate the effect of electron correlations on the electronic structure and magnetic properties of the full Heusler alloy Mn${}_2$NiAl in the framework of first-principles calculations. We investigate the electron correlation effect as employed within hybrid functional (HSE) and also within the DFT+U method with varied values of parameters between 0.9 and 6 eV. The XA-crystal structure was investigated with antiferromagnetic orderings of the magnetic moments of the manganese. It was found that with a growth of the Coulomb interaction parameter, the manganese ions magnetic moment increases, and it reaches the value of 4.15–4.46 ${\mu }_B$ per Mn. In addition, the total magnetic moment decreases because of the AFM ordering of the Mn ions and a small magnetic moment of Ni. The calculated total magnetic value agrees well with recent experiments demonstrating a low value of magnetization. This experimental value is most closely reproduced for the moderate values of the Coulomb parameter, also calculated in constrained LDA, while previous DFT studies substantially overestimated this value. It is also worth noticing that for all values of the Coulomb interaction parameter, this compound remains metallic in its electronic structure in agreement with transport measurements. Full article

In this article, the structural, elastic, electronic, and magnetic characteristics of both regular and inverse Heusler alloys, Sc₂TiAl and Sc₂TiSi, were investigated using a full-potential, linearized augmented plane-wave (FP-LAPW) method, within the density functional theory. The optimized structural parameters were determined from the minimization of the total energy versus the volume of the unit cell. The band structure and DOS calculations were performed within the generalized gradient approximation (GGA) and modified Becke–Johnson approaches (mBJ-GGA), employed in the Wien2K code. The density of states (DOS) and band structure (BS) indicate the metallic nature of the regular structure of the two compounds. The total spin magnetic moments for the two compounds were consistent with the previous theoretical results. We calculated the elastic properties: bulk moduli, $B$, Poisson’s ratio, $\nu$, shear modulus, S, Young’s modulus (Y), and the B/s ratio. Additionally, we used Blackman’s diagram and Every’s diagram to compare the elastic properties of the studied compounds, whereas Pugh’s and Poisson’s ratios were used in the analysis of the relationship between interatomic bonding type and physical properties. Mechanically, we found that the regular and inverse full-Heusler compounds Sc₂TiAl and Sc₂TiSi were stable. The results agree with previous studies, providing a road map for possible uses in electronic devices. Full article

Fully compensated ferrimagnets do not create any magnetic stray field and allow for a completely polarized current of charges. As a result, these alloys show promising prospects for applications as spintronic devices. In this paper, we investigated the phase stability, the site preference, the tetragonal distortion and the influence of symmetry from the crystal structure and chemical environments of magnetic ions on the magnetic properties of Cr₂YZ and Mn₂YZ (Y = void, Ni, Cu, and Zn; Z = Ga, Ge, and As) full Heusler alloys by first-principles calculations. We found that the selected Cr₂-based alloys, except for Cr₂NiGa and Cr₂NiGe, prefer to crystallize in the centrosymmetric L2₁-type structure, while the selected Mn₂-based alloys, except for Mn₂CuAs, Mn₂ZnGe and Mn₂ZnAs, tend to crystallize in the non-centrosymmetric XA-type structure. Due to the symmetry, the antiferromagnetism of the selected L2₁-type alloys is very stable, and no spin-polarized density of states could be generated. In contrast, the magnetic moment of the selected XA-type alloys depends heavily on the number of valence electrons and tetragonal distortion, and spin-polarized density of states is generated. Therefore, the selected alloys with L2₁-type structures and their tetragonal-distorted structure are potential candidates for conventional antiferromagnets, while those with XA-type structure and their tetragonal-distorted structure are promising candidates for (fully) compensated ferrimagnets. Full article

Based on the Hg₂CuTi structure, the full-Heusler alloy Ti₂CrSn, with a ground state band gap of semiconductor, is a thermoelectric material with potential applications. Through preparing Ti₂CrSn_1−xAl_x (x = 0, 0.05, 0.1, 0.15, 0.2) series bulk materials via arc melting, the effects of the electrical and thermal transport properties of Ti₂CrSn series alloys were investigated, and different Al doping on the phase structure, the microscopic morphology, and the thermoelectric properties of Ti₂CrSn were examined. The results show that the materials all exhibit characteristics of p-type semiconductors at the temperature range of 323 to 923 K. Al elemental doping can significantly increase the Seebeck coefficient and reduce the thermal conductivity of the materials. Among them, the sample Ti₂CrSn_0.8Al_0.2 obtained a maximum value of 5.03 × 10⁻³ for the thermoelectric optimal ZT value at 723 K, which is 3.6 times higher than that of Ti₂CrSn. Full article

In this work, we report the results of an experimental investigation on the synthesis, structure, microstructure, mechanical, electrical conductivity, and Seebeck coefficient of Co₂XSn (X = Zr, Hf) alloys. In both the alloys, the main constituent is a full Heusler-type compound that coexists with small amounts of secondary phases. Both alloys show a rather high Vickers hardness (around 900 HV) and an indentation fracture toughness typical of ceramics (around 2 MPa·m^1/2). The electronic transport properties of the two alloys were measured for the first time. The temperature dependence of both the Seebeck coefficient and the electrical conductivity of the two alloys shows a change in correspondence of the Curie temperature. The Seebeck coefficient reaches a constant plateau, while the electrical conductivities show a transition from metallic to semiconductor behavior. As a consequence, almost constant values of the power factor have been obtained for the power factor above the Curie temperature, which is promising for an efficient exploitation of thermal gradients of several hundreds of degree in waste heat harvesting applications. Finally, on the basis of results from this work and from the literature, the effect of the substitution of the X element on the electronic transport properties in the series Co₂XSn (X = Ti, Zr, Hf) is discussed. Full article

A hypothetical full-Heusler alloy, Sc₂VGe, was analyzed, and the comparison between the XA and L2₁ structures of this alloy was studied based on first-principles calculations. We found that the L2₁-type structure was more stable than the XA one. Further, the electronic structures of both types of structure were also investigated based on the calculated band structures. Results show that the physical nature of L2₁-type Sc₂VGe is metallic; however, XA-type Sc₂VGe is a half-metal (HM) with 100% spin polarization. When XA-type Sc₂VGe is at its equilibrium lattice parameter, its total magnetic moment is 3 ${\mathsf{\mu }}_{\mathrm{B}}$ , and its total magnetism is mainly attributed to the V atom. The effects of uniform strain and tetragonal lattice distortion on the electronic structures and half-metallic states of XA-type Sc₂VGe were also studied. All the aforementioned results indicate that XA-type Sc₂VGe would be an ideal candidate for spintronics studies, such as spin generation and injection. Full article

For theoretical designing of full-Heusler based spintroinc materials, people have long believed in the so-called Site Preference Rule (SPR). Very recently, according to the SPR, there are several studies on XA-type Hafnium-based Heusler alloys X₂YZ, i.e., Hf₂VAl, Hf₂CoZ (Z = Ga, In) and Hf₂CrZ (Z = Al, Ga, In). In this work, a series of Hf₂-based Heusler alloys, Hf₂VZ (Z = Al, Ga, In, Tl, Si, Ge, Sn, Pb), were selected as targets to study the site preferences of their atoms by first-principle calculations. It has been found that all of them are likely to exhibit the L2₁-type structure instead of the XA one. Furthermore, we reveal that the high values of spin-polarization of XA-type Hf₂VZ (Z = Al, Ga, In, Tl, Si, Ge, Sn, Pb) alloys have dropped dramatically when they form the L2₁-type structure. Also, we prove that the electronic, magnetic, and physics nature of these alloys are quite different, depending on the L2₁-type or XA-type structures. Full article