Half-metallic Properties Research Articles

DFT study with different exchange-correlation potentials of physical properties of the new synthesized alkali-metal based Heusler alloy

The aim purpose of this work is to investigate the various physical properties of the new synthesized alkali-metal based Heusler alloy Li2CoSb using the density functional theory. The results showed that the compound has ferromagnetic ground state and is mechanically stable against any small deformations. We performed calculations for different exchange-correlation potentials to obtain the magneto-electronic properties. The generalized gradient approximation (GGA) findings showed a metallic electronic nature with a weak magnetic moment. However, calculations by the modified Becke–Johnson exchange potential combined with GGA correlation (mBJ-GGA) indicated an increase in the magnetic moment but the alloy remains with a metallic character. To respect the strong electron correlation effect for the localized d states in the calculations, the mBJ-GGA + U scheme was used. The Half-metallic ferromagnetism behavior with integer total magnetic moment was found. The half-metallic property is preserved at a range 2–5 eV of Hubbard U parameter. The thermoelectric properties were calculated and divulged that the compound studied exhibit a high figure of merit, large Seebeck coefficient, and low thermal conductivity. Hence, the Li2CoSb is a good thermoelectric compound. The thermal and pressure effect on the isochoric and isobaric heat capacity and Debye temperature were studied using the quasiharmonic approximation. It is important to emphasis that all the investigated properties have not been studied yet for the present Li-based Heusler compound. Therefore, the present work can be considered as a first report.

Computational study of structural, electronic, half-metallic and thermodynamic properties of Sr3X2O7 (X = Fe, Mn) compounds

The structural, electronic, half-metallic and magnetic properties of Sr3Mn2O7, Sr3Mn2O7 and Sr3FeMnO7 have been investigated using the full-potential linearized augmented plane wave method. Besides, the thermodynamic properties of the materials of interest have been studied using the quasi-harmonic Debye model accommodating the lattice vibrations effects. Our results showed that Sr3Mn2O7 is an indirect half-metallic material with a band gap of 0.73 eV, while Sr3Fe2O7 and Sr3FeMnO7 exhibit a metallic behavior. The materials of interest are found to exhibit 100% spin polarization at the Fermi energy which make them potential candidates for electron-spin-based futuristic devices. The effect of pressure and temperature on the studied properties is found to be highly effective in tuning some of the macroscopic properties of the compounds in question. Our findings compare well with those existing in the literature.

Computational study of 4d transition metals doped bismuthene for spintronics

The new spintronic materials has earned extensive research attention due to their properties including faster data transfer, processing and storage. Espcially, antiferromagnets have fascinated due to their utilization in ultrafast spintronic devices. It has motivated us to explore the electronic and magnetic properties of buckled bismuthene doped with 4 d transition metals (TM) including Y, Zr, Nb, Mo, Tc, and Ru. The first principles calculations predicted the formation of covalent bond between dopant and host atoms. The doping of single 4 d-TM atom revealed that the magnetic moments show oscillating character due to hybridization of host-p and TM-d orbitals. The doping of Zr, Nb, Tc and the Ru in Bi appeared to produce spin polarized states with half metallic properties whereas Mo shown magnetic semiconductor. The doping of Nb in the matrix exhibited half mettalic behavior when dopant was placed at different sites. The single (S) and double (B) Mo-doped-Bi shown diluted magnetic semiconductor character except 2Mo–B-AFM. Remarkably, our calculations shown that 2Tc-S-Bi and 2Mo–S–Bi system appears ferromagnetic (FM) state, but 2Tc-B-Bi and 2Mo–B–Bi shows anti-ferromagnetism (AFM) state. A model presenting charge transfer and interaction between the impurities is proposed. Critical temperature investigation presents the probability of room temperature ferromagnetism from the structures. This study discloses that 4 d-doped Bi can be favorable applicant for potential applications in spintronic devices. • Structural, magnetic, and electronic properties of 4 d TM atoms doped bismuthene are systematically investigated. • Substituted doping can make bismuthen half-metallic or DMS or metal. • Magnetic half-metallic of Zr, Nb, Tc, Ru, substituted bismuthene systems can be realized by electronic or hole doping. • All 4 d-doped bismuthene systems can produce magnetism except Y doping. • The doping systems presents AFM, FM and NM coupling.

Elastic, Half-Metallicity, Thermodynamic, and Transport Properties of Ru2VGe and Ru2VSb Full-Heusler Compounds: a First-Principle Study

The aim of this work is the study of the magnetic, elastic, thermic, and thermoelectric properties of the ternary full-Heusler alloys Ru2VZ (Z = Ge and Sb) in L21 structure, using an ab initio calculation within the linearized augmented plane wave method with a full potential (FP-LAPW) based on the density functional theory (DFT). We computed these properties within the general gradient approximation (GGA). The structural parameters obtained are in favorable agreement with respect to the theoretical values found in the literature. The electronic properties studied have shown that the compounds have a half-metallic behavior. We have also computed the mechanical properties where we found that these full-Heusler compounds are mechanically stable. Furthermore, we have studied the thermal properties by the quasi-harmonic Debye model incorporated in the GIBBS code, which takes into account the lattice vibrations, pressure, and temperature effects on structural parameters. The thermoelectric properties were computed as a function of chemical potential at 300, 600, and 900 K. To our knowledge, the thermodynamic and thermoelectric characteristics have not yet been measured or calculated; hence, our results serve as a prediction for future study. Our obtained results for these quantities make these compounds attractive candidates for materials used in spintronic devices.

Optical, half-metallic and thermoelectric properties of the Co2TaAl [001] film

Based on the density functional theory framework and GGA approximation, the structural, electronic, optical and thermoelectric properties of the Co2TaAl and its [001] films have been calculated. The Co2TaAl compound has great hardness with the bulk modulus of 201.5 GPa which is bigger than steel. This compound has half-metallic nature with 100% spin polarization in the Fermi surface and 2.0µB magnetic moment. Due to its the real and imaginary dielectric function responses in the visible region and very low Eloss and extinction, this compound is a suitable case for optical applications in visible area energy. The Co2TaAl, also has a suitable thermoelectric efficiency in all temperatures, for a spin down with big power factor in high temperatures which is suitable for power generation applications. The energy-volume and thermodynamic phase diagrams of the [001] films are indicate, their stability, in the mechanical and thermodynamic views. The electronic diagrams showed the half-metallic behavior of the TaAl termination with 100% spin polarization, by the 0.25 eV energy gap in the down spin. The optical response of the TaAl termination for the E⊥z direction is similar to that of the bulk case and has a red shift, but in the E∥z the metallic nature is reduced. The merit amount of the TaAl termination is 0.7 in the lower temperatures for a down spin and its Seebeck has been greater than that of the bulk case.

Site preference, magnetic and electronic properties of half-metallic Vanadium-based full Heusler alloys

We reported a new atomic site preference occupation for Vanadium-based X2YZ full Heusler alloys. It tells that alloys with less 24 valence electrons form the L21-type structure, while others form the XA-type structure. This fact means that the site preference rule for Vanadium-based alloys depends on the total number of valence electrons instead of the electropositive between X and Y atoms. The magnetic moments of XA-type alloys follow the Slater-Pauling rules, with two forms, Mt = NV − 24 and Mt = NV − 18 corresponding to different origins of the band gaps. XA-type V2YZ (Y = Cr, Mn and Fe; Z = Ga, Ge and As), V2CoGa, V2CoGe and V2NiGa alloys have half-metallic property. L21-type V2YZ (Y = Cu and Zn; Z = Ga, Ge and As) alloys show no spin polarization and no half-metallic property due to the structural symmetry and the non-magnetism of copper and zinc atoms.

First-principles study of half-metallicity bulk rocksalt structure of CsTe and its surfaces

We report on the calculation of the structural, electronic, magnetic and half-metal properties of the rocksalt CsTe compound using the first principles method which is based on density functional theory. Although this compound does not possess any transitional metal in its formula, it is found to carry the half-metallic ferromagnetic property at bulk as well as the surfaces. The energy gap is equal to 3.32 eV at the equilibrium lattice constant of 7.7 Å. The formation energy is calculated to be -2.91 eV which reveals that this compound is stable. All the above-mentioned properties with the remarkable features open up the possible employment of the investigated material in several applications related to spintronics.

Theoretical Prediction of Half-Metallic Properties of CrHfCoZ (Z = Ga, In, Tl, Si) Alloys

Using first-principles calculations, we investigate systematically the stability, electronic and magnetic characteristics for the CrHfCoZ (Z = Ga, In, Tl, Si) alloys. Stability is estimated in views of thermodynamics, mechanical and dynamics points. Electronic calculations show that CrHfCoZ alloys have half-metallic behavior, and their integral magnetic moments obey the Slater-Pauling rule. Further, we discuss the formation of spin-flip gap along with integer magnetic moment according to the density of states. In addition, we plot the Fermi surface to illustrate the electronic behavior around the Fermi level of CrHfCoZ alloys. Finally, the changes of conduction band maximum and valence band minimum dependent on the lattice constants are also discussed. Our research may provide a potential applications in spintronic devices.

Computational Study of Structural, Electronic, Elastic, Half-Metallic and Thermoelectric Properties of CoCrScZ (Z=Al, Si, Ge, and Ga) Quaternary Heusler Alloys

The structure, electronic, half-metallic, elastic, and thermoelectric properties of the innovative quaternary Heusler (QH) CoCrScZ (Z=Al, Si, Ge, and Ga) alloys are studied by using density functional theory (DFT). CoCrScZ (Z=Al, Ga, and Ge) 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 results of half-metallic robustness show that the mechanical stability and half-metallicity of CoCrScZ (Z=Ga and Al) can be well maintained in the range of 5.79 to 6.28 A and 5.84 to 6.33 A, respectively. The QH CoCrScSi has a magnetic moment of 4.0 μB at the equilibrium lattice constant a = 6.04 A. The calculated Cauchy pressure, Pugh, and Poisson ratio prove that all alloys are hard, elastically ductile, and anisotropic. In addition, the temperature-dependent thermoelectric properties have been studied by calculating the electronic thermal conductivity (κ), Seebeck coefficient (S), power factor (PF), and electrical conductivity (σ/τ). High ZT values of 0.15, 0.12, 0.77, and 0.83 were obtained for CoCrScSi, CoCrScGe, CoCrScAl, and CoCrScGa, respectively. Based on our calculations, CoCrScZ (Z=Al, Ge, and Ga) combine both good spintronic and thermoelectric behaviors that may be used in spin injection applications.

Study of half metallic nature and transport properties of XMnSe2 (X = Ca, Sr and Ba) compounds via ab-initio calculations

In this work, we examine the half-metallic nature, optical and transport properties of ternary manganese selenides XMnSe2 (X = Ca, Sr and Ba) by means of the ab-initio calculations. Hexagonal structures of these selenides have been explored using generalized gradient approximation (GGA) and predicted ground states parameters exhibits good agreement with experimental data. Half-metallic nature of studied ternary manganese selenides is confirmed by investigating band structure with spin polarized density of states (DOS). In addition, half-metallic nature has been investigated in terms of integer values of the magnetic moment. Materials response toward electromagnetic radiation of energy 0−60 eV is calculated in terms of dielectric constant. Minimum loss of energy and maximum absorption of electromagnetic radiation at low energy region make these materials applicable to Infra-red (IR) devices. Transport properties are also calculated by using BoltzTraP code at temperature 0–800 K. Our computed results of half-metallic nature and transport properties have been suggested that studied ternary manganese selenides play vital role in the field of spintronic and energy devices.

Surface Effect on the Half-Metallic and Thermoelectric Properties of Co2TiSn [001] Film

The half-metallic, mechanical, and thermoelectric properties of the Co2TiSn in bulk and [001] films were investigated based on density functional theory (DFT) and full-potential linear augmented plane waves plus local orbitals method (FP-LAPW+LO). The exchange-correlation functional was approximated by generalized gradient approximation (GGA). The Co2TiSn bulk has mechanical stability in three static, dynamic, and elastic forms. All phonon branches have positive frequencies, and elastic results have shown the hardness with brittle behavior for this case. The Co2TiSn has half-metallic nature with full spin polarization at the Fermi energy and 2.0 μB magnetic moment. It also has a good figure of merit (ZT) about one that makes it suitable for thermoelectric applications. All four Co–Co, Co–Sn, Ti–Sn, and Ti–Co terminations of the [001] films have the ground state point. However, the Ti–Sn termination has half-metallic property so that in the up-spin it is metal and in the down-spin it is a semiconductor with an indirect energy gap of 0.3 eV. The thermoelectric behavior of the Ti–Sn termination has shown big Seebeck coefficient S with a positive sign and in lower temperatures, and the ZT amount around one in this temperature range. Moreover, the power factor (PF) of this case has a significant peak in the room temperature.

First-principles calculations of finite temperature electronic structures and transport properties of Heusler alloy Co2MnSi

In this study, we calculate the temperature-dependent electronic structures and transport properties of the Heusler alloy Co2MnSi on the basis of the Korringa–Kohn–Rostoker Green's function method combined with the coherent potential approximation (CPA). Temperature effects often have a significant influence on the spin-polarization properties of Heusler alloys. To incorporate the contributions of temperature effects, we first consider lattice vibrations and spin fluctuations. Using CPA, we can replace them with random displacements due to local phonons and local magnetic moment disorders, respectively. In the Co2MnSi Heusler alloy, we found that the band structures are smeared by the electron–phonon scattering process and the half-metallic property is eliminated by magnon excitations from the spin-up to spin-down states. Furthermore, we can estimate the electrical resistivity as a function of temperature in the scheme of linear response theory. Including the local phonon disorder, local moment disorder, and Mn–Co antisite disorder in CPA, we can reproduce the temperature-dependent resistivity observed by experiments.

Molecular and atomic adsorptions of hydrogen, oxygen, and nitrogen on defective carbon nanotubes: A first-principles study

To investigate the application properties of defective carbon nanotubes (CNTs) with gas adsorbates, structural and electronic properties after physical and chemical adsorptions of molecular and atomic hydrogen, oxygen and nitrogen on vacancy defects for capped single-walled carbon nanotubes (SWNTs) were simulated. The defective CNT shows the half-metal properties, but molecular chemisorption could convert the electronic property back to semiconductor. For the physisorptions of gas molecules, H2 is unstable for the endothermic process. If gas molecules approach to the defect in angstrom range, the chemisorption could happen, and oxygen molecule gains nearly 2 electrons. CNT work function drops with chemisorptions of molecular or atomic hydrogen, while oxygen behaves opposite. The weaker nitrogen chemisorption is able to keep oxygen away from adsorbing as the protective agent. The adsorption of atomic nitrogen may fill in the missing carbon atom to “repair” the defect and reduce the work function by 0.83 eV.

Structural, Electronic, Magnetic, and Optical Properties of Ir2ScZ (Z = Si, Ge, Sn) Full-Heusler Compounds: A First-Principles Study

The structural, electronic, magnetic, and optical properties of the full-Heusler compounds Ir2ScZ (Z = Si, Ge, Sn) have been investigated using density functional theory (DFT). For these compounds, the structure of type a is the most stable and their ferromagnetic phases are more stable rather than their antiferromagnetic or nonmagnetic phases. Spin-polarized calculations reveal that Ir2ScSi and Ir2ScSn follow the Slater–Pauling rule and have an integer magnetic moment of 1.00 $$ \mu_{\rm{B}} $$ at equilibrium lattice constant, while for Ir2ScGe it is 0.98 $$ \mu_{\rm{B}} $$ . The compound Ir2ScSi shows half-metallic properties at equilibrium lattice constant and under stress. Ir2ScGe and Ir2ScSn show half-metallic properties under stress. The Curie temperature of Ir2ScSi, Ir2ScGe, and Ir2ScSn is calculated to be 654.5 K, 537.6 K, and 633.4 K, respectively, and the half-metallic bandgaps are found to be 0.41 eV and 0.09 eV for Ir2ScSi and Ir2ScSn, respectively. The high Curie temperature and the half-metallic properties under stress of these compounds show that they are good candidates for use in spintronic devices and spin valves. The optical properties of Ir2ScSi at equilibrium lattice constant $$ a_{0} $$ and for Ir2ScGe and Ir2ScSn at $$ a_{4} = a_{0} - 4\% a_{0} $$ are investigated. For these compounds, rather high absorption occurs in the infrared region.

Bulk and surfaces half-metallicity of RbSe with zinc-blende structure: first-principles study

In this paper, the electronic, magnetic, and half-metallicity characteristics of the bulk as well as (111) and (001) surfaces of zinc-bland RbSe compound are explained using the first-principles calculations. All of calculations are performed through GGA approximations, and the results reveal that both the bulk and ends of the surfaces preserve the half-metallic property. In addition, the stability of the surfaces is computed. It is discovered that the Rb-terminated (001) is the most stable one compared to other terminates. Based on the magnetic characteristic computations, the spin magnetic moment of bulk is equal to 1 µB, while this value has changed at the surfaces due to the effects of surface states. All of the above-mentioned properties mark this compound as a suitable promising candidate for spintronics applications.

The effect of structural changes on the half metallic properties by using Tran Blaha modified Becke Johnson (TB_mBJ) method

One of the fields spintronics is dealt with nanoelectronic devices that reduce power consumption and increase memory with the help of spin polarized electrons. Therefore, both half-metal ferromagnet materials and non-magnetic materials created by spin injection from half-metal ferromagnets can also be used in spintronic applications. We wondered whether Co2ReSb, MnCoReSb, CoMnReSb and Mn2ReSb compounds that have not been studied experimentally and theoretically are suitable materials for use in spintronic applications. The half-metal ferromagnetic predictions of compounds were investigated by using Wien2k programme in Tran Blaha modified Becke-Johnson (TB_mBJ) method. First, the volume-energy optimization curves were plotted and observed that FM phases were the most stable energetically. Then the total magnetic moments of Co2ReSb and Mn2ReSb compounds were obtained as 2.00 µB/f.u. while these were 4.00 µB/f.u. in MnCoReSb and CoMnReSb compounds. Finally, the elastical studies showed that each compound was elastically stable because the stability conditions were satisfied. Therefore, Co2ReSb, MnCoReSb, CoMnReSb and Mn2ReSb compounds are half-metal ferromagnetic materials and they can be new candidates for using in spintronic applications.

GGA and GGA Plus U Study of Half-Metallic Quaternary Heusler Compound CoCrScSn

The structural, mechanical, electronic, magnetic, and half-metallic properties of quaternary Heusler compound CoCrScSn are studied using the GGA and GGA+U method based on first-principles calculations. It is found that Type-I structure of CoCrScSn compound is the most stable, and its ground state is ferromagnetic. At the equilibrium lattice constant, the electronic structures obtained by GGA and GGA+U methods indicate that CoCrScSn compound have typical half-metal character. The results of elastic constants and half-metallic robustness show that the mechanical stability and half-metallicity of CoCrScSn can be well maintained in the range of 6.2 to 6.9 Å under GGA and 5.7 to 6.4 Å under GGA+U, respectively. When CoCrScSn compound exhibits half-metallic properties, the total magnetic moment per molecular unit is 4.0 μB, which is in good agreement with the Slater-Pauling rule, and Cr atoms are the main source of molecular magnetic moment. All the aforementioned results indicate that quaternary Heusler compound CoCrScSn would be an ideal candidate in spintronics.

Improving the magnetic, electronic and optical properties of the monolayer WSe2 via Mn-X (X = O, S, Se or Te) codoping

The structural, magnetic, electronic and optical properties of the pure and Mn-X (X = O, S, Se or Te) codoped monolayer WSe2 systems are quantitatively examined through first-principles calculations. The lower formation energy under Se-rich condition shows that the codoped systems under Se-rich condition is more stable than W-rich condition, especially the Mn-O codoping is the most stable with the minimum formation energy -2.08 eV. Although the pure monolayer WSe2 is a nonmagnetic semiconductor, the codoped systems are all magnetic with total magnetic moments of 1.00 µB due to the introduced one unpaired electron. It is worth mentioning that the Mn-Se and Mn-Te codoping make the monolayer WSe2 display magnetic half-metallic properties. Finally, the optical properties of the pure and codoped monolayer WSe2 are studied in x (parallel to the WSe2 plane) and z (perpendicular to the WSe2 plane) directions. An interesting red-shift phenomenon has been observed in the curves of imaginary part of the dielectric function and absorption spectra for the Mn-X codoping, suggesting their quite promising applications in optoelectronic devices.

New equiatomic quaternary Heusler compounds without transition metals KCaBX (X = S and Se): Robust half-metallicity and optical properties

It is known that high spin-polarization and magnetism can be found even in materials with neither transition metals nor rare earths. In this paper, we report results of the structural design, electronic structure, magnetic and optical properties of new equiatomic quaternary Heusler (EQH) KCaBX (X = S and Se) compounds. Electron exchangecorrelation interactions are described by the Wu-Cohen (WC) functional and Tran-Blaha modified Becke-Johnson exchange (mBJ) potential. Ferromagnetic ordering is stable for the cubic structure of space group F43 m in which the K, Ca, B and X atoms are located at 4c, 4d, 4a and 4b Wyckoff positions, respectively. Quaternaries at hand exhibit a perfect spin-polarization around the Fermi level, which is a result of the half-metallicity with metallic spin-up channel and semiconductor spin-dn channel. The ferromagnetic half-metallic and spin-flip band gaps are 2.648(2.470) and 0.673(0.526), respectively, for KCaBS(KCaBSe). Both studied compounds have a total magnetic moment of 2.000 μB. Additionally, the strain effect on the electronic and magnetic properties is also examined. Finally, the optical properties of the KCaBX alloys are investigated for energies up to 25 eV. Optical spectra show the metallic behavior at extremely low energies and semiconductor nature at higher energies. Interestingly, KCaBS and KCaBSe exhibit prospective absorption properties with a quite large absorption coefficient in the ultraviolet regime.

Robust intrinsic half-metallic ferromagnetism in stable 2D single-layer MnAsS4

Two-dimensional (2D) intrinsic half-metallic materials are of great interest to explore the exciting physics and applications of nanoscale spintronic devices, but no such materials have been experimentally realized. Using first-principles calculations based on density-functional theory, we predicted that single-layer MnAsS4 was a 2D intrinsic ferromagnetic (FM) half-metal. The half-metallic spin gap for single-layer MnAsS4 is about 1.46 eV, and it has a large spin splitting of about 0.49 eV in the conduction band. Monte Carlo simulations predicted the Curie temperature (Tc) was about 740 K. Moreover, within the biaxial strain ranging from −5% to 5%, the FM half-metallic properties remain unchanged. Its ground-state with 100% spin-polarization ratio at Fermi level may be a promising candidate material for 2D spintronic applications.