Half-metallic Alloys Research Articles

Half-metallic Na-based half-Heusler alloys as potential spintronic materials

Half-metallic Na-based half-Heusler alloys as potential spintronic materials

Enhancement of the thermoelectric performance of half-metallic full-Heusler Mn2VAl alloys via antisite defect engineering and Si partial substitution

A half-metallic full-Heusler Mn2VAl alloy is a potential p-type thermoelectric material that can directly generate electricity from waste heat via the Seebeck effect. For practical use, the Seebeck coefficient S of Mn2VAl should be increased while maintaining a high electrical conductivity σ from its half-metallic character. Herein, we achieved this objective through antisite defect engineering. Theoretically, it was predicted that the S was maximized by regulating partial density of states of majority-spin sp-electrons through the control of the fraction of antisite defect, fAD, between V and Al atoms in Mn2VAl. Experimentally, a significant increase in S and a slight decrease in σ were observed for an Mn2VAl sample with an optimal fAD = 33%, enhancing the thermoelectric power factor PF by 2.7 times from an Mn2VAl sample with fAD = 14%. Furthermore, we combined the antisite defect engineering with a partial substitution method. An Mn2V(Al0.96Si0.04) sample with fAD = 33% exhibited the highest PF = 4.5 × 10−4 W·m−1·K−2 at 767 K among the samples. The maximum dimensionless figure-of-merit zT of the Mn2V(Al0.96Si0.04) sample with fAD = 33% was measured to be 3.4 × 10−2 at 767 K, which is the highest among the p-type half-metallic full-Heusler alloys.

Computations on platinum based ternary ferromagnetic half metals for spin valve diodes and green energy technology based thermoelectric

The ab initio method commonly known as wavefunction method is used to calculate the structural, mechanical, electronic, magnetic, lattice dynamical and thermoelectric properties of the half metallic half-Heusler alloys VPtZ (Z = Si, Ge, Sn). The equilibrium lattice constants and corresponding ground state energies of the studied alloys are computed in stable ferromagnetic γ-phase with a cubic structure. The electronic properties suggest that the compounds are half metals with indirect band gap having the band energies of 1.02 eV, 1.04 eV and 0.9 eV for VPtSi, VPtGe and VPtSn, respectively, in the spin down channel. The materials have spin magnetic moment of 1 μB, suggest that the materials are suitable for making spintronic devices such as spin valve diodes. Temperature dependent heat transport properties were studied by using classical Boltzmann theory. The materials have high power factor at high temperatures. Thermoelectric performance of the materials is calculated between the temperature range 100–1200 K respectively. The obtained thermoelectric figure of merit for p-type VPtSi, VPtGe and VPtSn are 0.4, 0.7 and 0.3, respectively, at 1200 K. Similarly, the figure of merit obtained for n-type VPtSi, VPtGe and VPtSn are 0.41, 0.75 and 0.3, respectively, at the same temperature. The favourable energy and spin transport properties of these alloys show that they are the potential candidates as thermoelectric for heat energy harvesting and spintronic for magneto electronics applications.

Computational Insights into the Structural, Electronic, Mechanical, Magnetic, and Thermodynamic Properties of New Half-Metallic Ferromagnetic Full-Heusler Alloys Cr2HfZ (Z = Ge, Sb, and Pb) Using FP-LAPW Method

Computational Insights into the Structural, Electronic, Mechanical, Magnetic, and Thermodynamic Properties of New Half-Metallic Ferromagnetic Full-Heusler Alloys Cr2HfZ (Z = Ge, Sb, and Pb) Using FP-LAPW Method

Insight into the structural, electronic, mechanical, magnetic and thermodynamic properties of the new half-metallic ferromagnetic full-Heusler alloys Cr2YZ (Z = Si, Ge, Sn) from initio calculations

Insight into the structural, electronic, mechanical, magnetic and thermodynamic properties of the new half-metallic ferromagnetic full-Heusler alloys Cr2YZ (Z = Si, Ge, Sn) from initio calculations

Enhancement of thermoelectric performances in n-type RbCrZ (Z = S, Se, Te) half-metallic ferromagnetic alloys via charge carrier concentration or chemical potential

We used first-principles simulations to examine the magnetic, elastic, and thermoelectric properties of RbCrZ (Z = S, Se, and Te) half-Heusler alloys. Our results indicate that RbCrZ (Z = S, Se, and Te) alloys are completely spin-polarized half-metallic ferromagnets in the ground state. Elastic constants provide mechanical stability. Unlike RbCrS and RbCrSe, RbCrTe is brittle and unable to withstand thermal shocks. RbCrS is the most anisotropic material, while RbCrSe is the most isotropic. The greatest ZT values in the spin-down channel for RbCrS, RbCrSe, and RbCrTe are 0.81355, 0.62249, and 1.02846, respectively. To attain this value, the charge carrier concentration must be lowered to n = - 3.18119 × 1022 cm−3 for RbCrS, n = - 5.32817 × 1022 cm−3 for RbCrSe, and for RbCrTe, the charge carrier concentration must be enhanced to n = - 4.99321 × 1022 cm−3. The decrease of the chemical potential of RbCrS, RbCrSe, and RbCrTe by 0.02, 0.084, and 0.0329 Ryd, respectively, resulted in identical values.

Itinerant magnetism, electronic properties and half-metallicity of Co2ZrSn and Co2HfSn Heusler alloys

Half-metallic ferromagnetic alloys are attracting considerable interest for their potential applications in spintronic devices. Co-based Heusler alloys are considered to be promising half-metallic compounds as they combine suitable magnetic, electronic and transport properties with compositional versatility and high thermal stability. In this work, Co 2 ZrSn and Co 2 HfSn Heusler alloys were studied by combining experimental and ab-initio investigations in order to accurately estimate their electronic density of states in proximity of the Fermi level and to determine their magnetic and electronic properties. Magnetization measurements, performed between 2 K and 550 K, suggest for both alloys a gradual transition from localized ferromagnetism to weak itinerant ferromagnetism with increasing temperature, well described by a simple mean field model up to the Curie temperature (454 K in Co 2 ZrSn and 432 K in Co 2 HfSn) and beyond. Ab-initio calculations were performed using two exchange-correlational functionals, PBE and PBE optimized for solids (PBEsol), in order to assess the reproducibility of theoretical results. Overall, band structures and density of states (DOS) diagrams indicated, for both compounds, the presence of a half-metallic band gap in the minority spin sub-band. The dependence of magnetic moments and band gap width on cell parameters is discussed in detail. Calculated magnetic moments and cell parameters satisfactorily match the experimental results obtained in this work and previously reported in the literature. • Itinerant weak ferromagnetic behaviour is confirmed for both alloys as they follow the Edwards-Wohlfarth model. • The mean field model indicates that the density of states profiles at the Fermi level are smooth. • Ab-initio calculation performed with PBE and PBEsol functionals show half-metallic behaviour at 0 K. • A crossover from localized magnetism to itinerant magnetism as function of temperature was found for both alloys. • The M/T crossover can be attributed to a change in spin-flip mechanism at low temperature.

Half-metallic p0-d half-Heusler alloys with stable structure in ferromagnetic state

We investigate the structural, magnetic, thermodynamic, and mechanical stability of p0-d half-Heusler compounds composed of p0 = Li, Be, Na, Mg alkali and alkaline earth metals; 3d transition metals; and group V (pnicogens) & VI (chalcogens) sp atoms using the DFT based full-potential Wien2k package. Ferromagnetic, antiferromagnetic, and non-magnetic calculations are performed to ascertain the stable magnetic state. From 280 compounds under study, 16 of them show half-metallic properties in the minimum-energy half-Heusler phase at the optimized lattice constant. Calculations show that compounds are stable in the half-Heusler β-phase and the ferromagnetic state. The band structure and the density of states are obtained for both GGA and GGA + U exchange correlation approximations. Furthermore, in order to study the thermodynamic and the mechanical (dynamic) stability of the compounds, the formation energy, the hull distance, and the elastic constants of half-metallic compounds are calculated. The estimated coupling constants and Curie temperatures from Monte Carlo simulations show that these compounds preserve the ferromagnetic state and magnetic polarization at temperatures much higher than the room temperature and may well be suitable materials for spintronic applications. The phonon dispersion curve for NaVBi as the compound that has the highest Curie temperature among half-metallic compounds shows no imaginary frequencies and testifies to the dynamic stability of the compound in the ferromagnetic half-Heusler β-phase as expected from the elastic constants.

Structural, electronic and magnetic properties of the Half-Heusler alloy CrZSi (Z = Sc, Ti)

The structural, electronic and magnetic properties of the half-Heusler alloys CrZSi (Z = Sc, Ti) were studied using Density Functional Theory (DFT) based on pseudopotential method to explore the Cr-based ferromagnetic half-metallic alloys. The effect of substitution of scandium and titanium in Slater-Pauling behaviour, half-metallicity and mechanical properties were studied to understand the role of low valent transition element in half-Heusler compound. CrTiSi shows half-metallicity with an indirect bandgap of the value 0.765 eV. The robustness of half-metallic behaviour at different hydrostatic pressures were calculated. CrTiSi obeys Slater-Pauling rule and has integer magnetic moment of 4 μB. The mechanical properties were studied for both CrScSi and CrTiSi compounds to obtain elastic constants and moduli. The present work reveals the ductile nature of the compounds as their B/G ratio is >1.75 with positive Cauchy pressure. Further, phonon calculation with absence of negative frequencies determines the dynamical stability of the compound.

First-principles calculations to investigate structural, elastic, electronic and magnetic properties of novel d0 half metallic half Heusler alloys XSrB (X=Be, Mg)

The structural, elastic, electronic properties and magnetism of new d0 half Heusler alloys XSrB (X = Be, Mg) were investigated by means of first-principles calculation based on the density functional theory (DFT). The exchange-correlation functional is treated by the generalized gradient approximation proposed by Perdew–Burke–Ernzerhof (GGA-PBE). The Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange potential, which can compute accurately the band gap of solids, is adopted to improve the calculations of the electronic structure and magnetic properties. We found that the two alloys are energetically and mechanically stable in the α phase presenting ductile nature with negative cohesive energies. It was found that MgSrB compound can be experimentally synthesized because of its negative formation energy. The two compounds are half-metallic ferromagnets with total magnetic moment of 1.000 μB per formula unit, in well agreement with Slater-Pauling rule (Mtot = (8 – Ztot) μB). Our calculations show that BeSrB and MgSrB have majority band gaps of 1.024 eV (1.387 eV) and 0.831 eV (1.277 eV) with half-metallic gaps of 0.165 eV (0.613 eV) and 0.311 eV (0.626 eV), respectively, by GGA-PBE (TB-mBJ). The origin of these gaps is well discussed. It was also found that BeSrB and MgSrB are robust half-metallic alloys with respect to the variation of lattice constants. They kept their half-metallicity in relatively wide range of lattice constants of 5.90–7.00 Å and 6.18–7.28 Å, respectively. The obtained results reveal also that BeSrB and MgSrB compounds are considered as nearly gapless half-metallic ferromagnets for lattice parameters range of 7.03–7.88 Å and 7.50–8.40 Å, respectively, which makes them promising candidates for potential applications.

Ab-initio investigation of structural, mechanical, thermodynamic, electronic, magnetic and thermoelectric properties of half-metallic d0 half-Heusler alloys LiXSi (X=Ca, Sr)

Structural, mechanical, thermodynamic, electronic, and magnetic properties of LiXSi (X ​= ​Ca, Sr) d0 half-Heusler alloys have been evaluated by implementing the GGA-PBE approximation in the Density Functional Theory calculations. The Boltzmann transport theory has been implemented for examining the thermoelectric properties of the alloys. The spin-polarized calculations show that LiCaSi and LiSrSi crystallize in the ferromagnetic α-phase equilibrium states. Spin-resolved band structures depict complete spin polarization obtained at the Fermi level and confirm the true half-metallic nature of the alloys. The calculated total magnetic moment is 0.99 ​μB for LiCaSi and 1.00 ​μB for LiSrSi, which very closely follow the Slater-Pauling rule. The observed ferromagnetic characteristics arise mostly from the spin-polarization of the 2p states in Si for both alloys. The LiXSi (X ​= ​Ca, Sr) alloys are found to be mechanically stable according to the Born stability criteria for cubic structured systems. Both the alloys are predicted to be ductile in nature. Important thermodynamic properties such as Debye temperature and CV have been calculated by implementing the quasi-harmonic approximation. The calculations for the transport properties show that the alloys are p-type materials with high Seebeck coefficients and electrical conductivities. The dimensionless thermoelectric figure of merit obtained for both the alloys at 300K is close to unity, which confirms the high thermoelectric efficiency of the alloys.

Investigation of electronic, optical, and thermoelectric properties of new d0 half-metallic half-Heusler alloys SiLiX (X = Ca and Sr)

Investigation of electronic, optical, and thermoelectric properties of new d0 half-metallic half-Heusler alloys SiLiX (X = Ca and Sr)

Computational investigation of half-Heusler/MgO magnetic tunnel junctions with (001) orientation

A series of half-metallic XYZ half-Heusler alloys is combined with MgO to create Heusler–MgO junctions. The electronic and magnetic properties of these junctions are investigated. The strong oxidation between metal and oxygen atoms causes the systems with pure YY interfaces to be the most stable cases. We conclude that uniaxial anisotropy can be induced in Heusler layers adjacent to MgO. The type of interface layers determines the half-metallicity and anisotropy (in-plane or perpendicular) in the Heusler–MgO junctions. The capacity to retain both half-metallicity and perpendicular magnetic anisotropy in NiMnSb/MgO and CoTiSn/MgO junctions with a MnMn interface layer makes these structures potential candidates as electrode layers in spin transfer torque random access memory devices.

Insight view of double perovskites Ba 2 XNbO 6 (X = Ho,Yb) for spintronics and thermoelectric applications

Considering accelerated discovery of half-metallic alloys has substantially created a research curiosity due to their potential technological considerations and multi-functional applications. In this work, we have delivered a theoretical overview on experimentally determined Ba2XNbO6 (X = Ho,Yb) alloys first time to understand their basic structural chemistry and other physical properties by Density Functional Theory (DFT). The exploitation of the Birch-Murnaghan equation to obtain their lattice parameters, designates a clear-cut consistency with the experimental results. Quantum description of identifying electronic structures of Ba2XNbO6 (X = Ho,Yb) is achieved by the insertion of Generalised gradient approximation (GGA), Hubbard correlation correction (GGA + U) and Tran-Blaha modified Becke-Johnson (TB-mBJ) potential. The exhibition of spin-polarisation creates ferromagnetism of (4 and 1) μB respectively has been put forwarded in this report. Moreover, phonon dispersions decisively certifies the dynamical stability by using density functional perturbation theory (DFPT). The Seebeck coefficient of Ba2HoNbO6 (Ba2YbNbO6) obeys half-metallic trend with their outcomes values at room temperatures −347.65 μV/K (−261.11 μV/K) in spin-up and −69.29 μV/K (3.42 μV/K) in spin-dn respectively. The summed-up properties catch a magnificent and dynamic view to see these alloys in spintronics and thermoelectric progressive technologies.

Theoretical design of novel half-metallic alloys XMg3O4(X = Li, Na, K, Rb)

Theoretical design of novel half-metallic alloys XMg3O4(X = Li, Na, K, Rb)

Structural, electronic, elastic, magnetic, phonon and thermodynamic properties of inverse-Heusler-Ti2FeX (X=Si, Ge, and Sn): Insights from DFT-based computer simulation

The structural, mechanical, electronic and lattice dynamic properties of Ti2FeX (X = Si, Ge, and Sn) inverse-Heusler alloys have been explored via first-principles calculations based on density functional theory. The equilibrium lattice constant, bulk modulus, electronic band structure and magnetic moment values of these alloys have been computed to be consistent with prior studies. Several mechanical parameters such as elastic constants Cij, bulk modulus B, Young modulus E, shear modulus G and Poisson’s ratio υ are calculated, and based on these calculations, mechanical stability is examined. The calculated values of the total magnetic moments are in close agreement with the existing theoretical data and comply with the Slater-Pauling rule. From their calculated electronic band structure, Ti2FeSi, Ti2FeGe and Ti2FeSn are found as half-metallic alloys at the equilibrium lattice constant with a minority-spin energy gap of 0.820, 0.850 and 0.780 eV, respectively. The full phonon spectra, and their total and partial density of states of these alloys have been carried out via the direct method. The calculated phonon spectrum points out dynamic stableness of these alloys. Furthermore, the thermodynamic properties such as the heat capacity, thermal expansion, entropy and Grüneisen parameter have been investigated in the Debye model using the Gibbs2 code with a series of temperature from 0 to 1500 K.

The structural, electronic, magnetic, and optical properties of the Cr-, Mo-, and W-doped ZnTe alloys

The first-principle method is adopted to study doping of different atoms X (X = Cr, Mo, or W) in ZnTe compound. The spin-down bandgaps of the X-doped Zn0.96875X0.03125Te alloys are 1.368, 1.415, and 1.399 eV for X = Cr, Mo, and W, respectively. All the doped Zn0.96875X0.03125Te (X = Cr, Mo, or W) alloys presents half-metallic (HM) feature, which is different from the ZnTe semiconductor, thus the doped HM alloys are the potential materials for spintronic applications. The Cr-3d(t2g) and Te-5p spin-up states of the Zn0.96875Cr0.03125Te alloy intersect the Fermi level, but only the Mo-4d(t2g) and W-5d(t2g) spin-up states of the Zn0.96875Mo0.03125Te and Zn0.96875W0.03125Te alloys, respectively, intersect the Fermi level. For the Zn0.96875Cr0.03125Te alloy, the double-degenerate $$d_{yz}$$ and $$d_{xz}$$ spin-up states of Cr atom are occupied, but the undegenerated $$d_{xy}$$ states of Cr atom are unoccupied. But for Zn0.96875X0.03125Te (X = Mo or W) alloys, the threefold degenerate $$d_{xy}$$ , $$d_{yz}$$ , and $$d_{xz}$$ states of X atoms are half-occupied. All the X-doped Zn0.96875X0.03125Te (X = Cr, Mo, or W) alloys are magnetic with the total magnetic moments of 4.000 $$\mu_{{\text{B}}}$$ mainly contributed by the X atom and neighboring Te atoms. The doped Zn0.96875X0.03125Te (X = Cr, Mo, or W) alloys have promising applications in infrared devices.

Structural and mechanical stability, lattice dynamics and electronic structure of the novel CrVZ (Z = S, Se, & Te) half-Heusler alloys

To meet energy demand, half-Heuslers (HH) are proved to be a cost-effective and energy-efficient choice for advanced spintronic and energy storage applications. The structural, electronic, magnetic, vibrational, elastic, thermodynamic and thermoelectric properties of the innovative HH CrVZ (where Z = S, Se, & Te) alloys are studied by using density functional theory (DFT). All materials are found to be magnetically active with 100% spin polarization where partially filled 3d-orbitals of Cr confirm the major contribution to the magnetic moment. The ferromagnetic (FM) state is observed to be the most energetically stable state among the non-magnetic (NM) and antiferromagnetic (AFM) states for all the HH CrVZ alloys with their optimized lattice parameters ranging from 5.47 Å to 6.00 Å. The HH CrVSe alloy is found to have the lowest direct bandgap (EBG) of 1.07 eV with a comparatively highest half-metallic gap (EHM) of 0.44 eV, due to the d-d hybridization. Our calculated cohesive (EC) and formation (Ef) energies indicate the chemical and thermodynamic stability of the studied HH CrVZ alloys. The phonon dispersion curves for the HH CrVSe and CrVTe alloys show that they are vibrationally stable while HH CrVS alloy shows soft modes with imaginary frequency due to the small ionic size of the S-ion. The calculated Cauchy pressure, Pugh and Poisson ratio prove that all studied compounds are hard, elastically brittle, anisotropic, and mechanically stable. The temperature fluctuations for specific heat (CV), Entropy (S) and Free Energy (F) follows the Quasi-harmonic Debye model with expected Dulong-petit limit 75 J/mol/K. The thermoelectric investigations although show the lower values of the Seebeck coefficient and power factor. Our investigated half-metallic HH CrVZ alloys can be the potential contenders for the spintronic applications.

First-principles search for half-metallic ferromagnetism in CsCrZ2 (Z = O, S, Se or Te) Heusler alloys

Exploring highly spin-polarized materials is crucial for the development of spin-based devices. In this paper, we investigate the atomic structure, electronic, half-metallic and magnetic properties of the CsCrZ2 (Z = O, S, Se or Te) Heusler alloys, by performing first-principles calculations based on density functional theory (DFT). The geometry optimization process shows that the alloys are more stable in Cu2MnAl type structure than in Hg2CuTi one. To find a magnetic ground state, the total energy of the alloys is calculated in the non-magnetic (NM), ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering. We find that, the FM ordering yields the lowest energy, thereby confirming that the alloys are FM in the ground state. On computing the cohesive and formation energy in the ground state, it is found that alloys are chemically and thermodynamically stable, respectively. Spin polarized band structures and density of states (DOS) demonstrate that the CsCrO2, CsCrS2 and CsCrSe2 alloys are true half-metals with 100% spin-polarization at the Fermi level, while the CsCrTe2 alloy is predicted as highly spin polarized material. Furthermore, the CsCrO2, CsCrS2 and CsCrSe2 alloys possess 2.529, 2.250 and 2.050 eV gaps in the spin down band structure, respectively. The calculated total magnetic moments reveal that half-metallic alloys have an integral total magnetic moment of 3.000 μB, which satisfies the Slater-Pauling rule Mt = Zt-16. The main contribution to the total magnetic moment comes from the Cr atoms (about 3.9 μB). Furthermore, the Curie temperature TC calculated within classical Heisenberg model is estimated to be about 822 K (CsCrO2), 685 K (CsCrS2), 753 K (CsCrSe2) and 636 K (CsCrTe2). The obtained high spin polarization and above room temperature FM ordering make the materials as promising materials to be used in spintronic technology.

Computational discovery of the novel half-metallic full-Heusler alloys Mn2LiAs and Mn2LiSb

The structural, elastic, electronic and magnetic properties of the novel full-Heusler alloys Mn2LiAs and Mn2LiSb are determined to explore their structural stability and half-metallicity. The method used is the first-principles method based on density functional theory. Calculations show that the Hg2CuTi-type structure is more energetically favourable than the conventional Cu2MnAl-type structure and is thermodynamically and mechanically stable for both alloys. The Hg2CuTi-type Mn2LiAs and Mn2LiAs alloys are half-metallic ferrimagnets and have a total magnetic moment of 2.000 μB per formula unit. They follow the Slater-Pauling rule and have an indirect energy gap in the spin-down channels with values of 1.176 and 1.269 eV at equilibrium lattice constants of 5.793 and 6.132 Å, respectively. The half-metallicity is kept within the limits of a wide lattice constant range. The spin polarisation ratio is 100% and the total magnetic moment is 2.000 μB. Mn2LiAs and Mn2LiSb alloys, which can be synthesised via experiments, are promising candidates for spintronic applications.