Free Space Charge Value Research Articles

First-principles study of the strain effect with half-metallic ferromagnetism in Cd 1−x V x Te alloys: supercell approaches

In this work, we study the effect of vanadium (V) dopantson the structural, electronic, and magnetic properties of the CdTe alloys using density functional theory (DFT). The calculations are performed as a function of the concentration of V in the host CdTe semiconductor using a 2 × 2 × 1 tetragonal supercell and a 2 × 2 × 2 cubic supercell. The lattice constants and bulk modulus of Cd 1−x V x Te alloys are determined. The analysis of the density of states shows that the Cd0.75 V0.25Te alloys in both supercells present a total polarization of 100% at the Fermi level, which confirms a stable half-metallic ferromagnetism phase in these materials, in contrast to the Cd 0.9375 V 0.0625 Te and Cd 0.875 V 0.125 Te alloys, which have a polarizability that does not reach 100%. In addition, the electronic band structures are used to estimate the s(p) − d exchange constants mainly resulting from the p − d hybridization between V- 3d and Te-p. Furthermore, the local magnetic moment of V of its free space charge value decreases, leading to the appearance of a small magnetic moment on the Cd and Te sites. Besides, the magnetic stability at different doping concentrations in the ferromagnetic (FM) and anti-ferromagnetic (AFM) states is examined, where the total energy of the systems is considered as a stability criterion. The robustness of the half-metallicity and the curie temperatures under the strain effect are also investigated. Finally, we rely on the binding energy to evaluate the energetic stability of the vanadium in the intrinsic compound CdTe under external deformations.

Spin-polarized electronic and magnetic properties of Ruddlesden-Popper Nd2MO4 (M = Sc and Y) compounds

The first principle calculations on the structural, electronic structure as well as the magnetic properties of Ruddlesden-Popper Nd2MO4 (M = Sc and Y) compounds were accomplished by using the full-potential linearized augmented plane waves with local orbitals (FP-LAPW + lo) method within the spin-polarized density functional theory (spin-DFT) and implemented in the WIEN2k package. The exchange and correlation potential was treated with the generalized gradient approximation PBE-GGA for the structural properties. Moreover, the PBE-GGA + U approximation (where U is the Hubbard correlation term) is used to treat “d” and “f” electrons for the electronic and magnetic properties of these compounds. The equilibrium structural parameters such as: lattice constants (a0 and c0), bulk modulus (B0) and the first pressure-derivative of bulk modulus (B’), are optimized for all these alloys. The calculations of the electronic properties for the Ruddlesden-Popper Nd2MO4 (M = Sc and Y) compounds at their equilibrium lattice parameters disclose that the both compounds are half-metallic materials. The magnetic properties show that the total magnetic moment for the two Nd2ScO4 and Nd2YO4 compounds is found in integer value. The magnetic moment of Nd is reduced from its free space charge value of 4μB, whereas small magnetic moments are produced on the nonmagnetic O1 and O2 sites.

Half-metallic ferromagnetism in Ga1-xCoxP (x = 0.125, 0.25, 0.75, and 1) alloys: An ab-initio study

III-V compounds belong to one of the most used materials in the technological applications. The doping of transition metals can induce magnetic properties in III-V for the use in spintronics applications. Effect of Co doping with different concentrations (0.125, 0.25, 0.75, and 1) on the physical properties of GaP is investigated using the spin dependent density functional theory. The equilibrium structural parameters such as the lattice constant (a0), the bulk modulus (B0) and the first pressure-derivative of the bulk modulus (B’) are optimized for all these alloys. The calculations of the electronic properties for the Ga1-xCoxP alloys at their equilibrium lattice parameters disclose that all Ga0.875Co0.125P, Ga0.75Co0.25P, Ga0.25Co0.75P, and CoP alloys are complete half-metallic materials. The magnetic properties show that the total magnetic moment for all Ga0.875Co0.125P, Ga0.75Co0.25P, Ga0.25Co0.75P, and CoP alloys has integer value. The p-d hybridization reduces the atomic magnetic moment of Co atom from its free space charge value of 2μB and creates weak local magnetic moments on the nonmagnetic Ga and P sites. Furthermore, the s(p)-d exchange coupling constants N0α and N0β constants are computed to understand role of exchange splitting process in conduction and valence bands. The high spin polarization and originating the ferromagnetism in GaP by the doping of Co can be valuable systems for the use in spin based applications in various electronic devices.

Semiconducting and magnetic properties within B(1-x)VxAs alloys at x = 0 and x = 0.25: A DFT + U study

The physical (mechanical (structural and elastic), electronic and magnetic) properties of the zincblende BAs parent compound and its B0.75V0.25As alloy are analyzed by employing the FP-L/APW + lo method as implemented in WIEN2k code, where the XC potential is approached by the GGA approximation. The analysis of the structural properties in B0.75V0.25As system indicates its stability in ferromagnetic state, where its computed equilibrium lattice parameters (the lattice constant (a0), the bulk modulus (B0), and the first-pressure derivative (B’) of the bulk modulus) are given. The elastic moduli (C11, C12, and C44) and anisotropy factor for the cubic system are determined for these compounds in the purpose to confirm their mechanical stability. The electronic structure of B0.75V0.25As shows its complete semiconducting feature. The electronic density of states indicates that the uncompleted 3d-V orbitals broaden on the width of the exchange splitting energies (Δx(d) and Δx(pd)); accordingly, the effective potential of minority-spin electrons are more attracted comparing to the majority-spin electrons. The magnetic properties unveil that the value of total magnetic moment of B0.75V0.25As alloy is found in an integer number. Thus, the hybridization between 3d-V and 4p-As states pushes to reduce the atomic magnetic moment of V element from its free space charge value and to produce local magnetic moments on B and As nonmagnetic sites. Moreover, the s-d exchange constant of conduction band (N0α) and the p-d exchange constant of valence band (N0β) are evaluated in the reason to know contributions during the exchange splitting process.

Density functional theory investigation of half-metallic ferromagnetism in V-doped GaP alloys

The spin polarized structural, electronic, and magnetic properties of zincblende Ga1−xVxP (x = 0, 0.25, 0.50, 0.75, and 1) alloys are studied by using the full-potential linearized augmented plane waves with local orbital (FP-L/APW + lo) method within the spin-polarized density functional theory (spin-DFT). The exchange and correlation (XC) energy is defined in all this approach by the generalized gradient approximation (GGA-PBE) of Perdew-Burke-Ernzerhof, whereas the GGA + U (U is the Hubbard term of the Coulomb repulsion correlation) functional is employed specially to treat and improve the electronic and magnetic properties of these compounds. The structural properties show the stability of Ga1−xVxP alloys in ferromagnetic phase, where their equilibrium structural parameters (lattice constant (a0), bulk modulus (B0), and its first-pressure derivative (B’) are evaluated. The elastic constants for the cubic system (C11, C12, and C44) and anisotropy are computed in the goal to prove the mechanical stability of these compounds. The electronic results reveal that both Ga0.25V0.75P and VP alloys have a perfect half-metallic nature, while the Ga0.75V0.25P alloy is a semiconductor. From band structures, we observe that the unfilled 3d-V orbitals increase the rise of spin-exchange splitting energy Δx(d) and Δx(pd); consequently, we found that the minority-spin case presents an attractive effective potential comparing to the majority-spin case. The total magnetic moment of Ga0.75V0.25P, Ga0.25V0.75P and VP alloys are found in integer value (2μB), affirming their complete half-metallic behavior. Moreover, we estimate the s-d exchange constant N0α (conduction band) and the p-d exchange constant N0β (valence band) to analyze contributions of conduction and valence bands in the exchange splitting process; in the other hand, the observed p-d hybridization reduces the atomic magnetic moment of V element from its free space charge value and produces weak local magnetic moments on the nonmagnetic sites of Ga and P atoms.

First-principles calculations to investigate half-metallic ferromagnetism in Zn0.50Ti0.50S alloy by using DFT + U calculations

ABSTRACTThe spin-polarized structural, electronic and magnetic properties of the Ti-doped zincblende ZnS compound at x = 0.50 (Zn0.50Ti0.50S alloy) have been investigated by employing the first-principles full-potential linearised augmented plane wave with local orbitals (FP-L/APW + lo) method within the frame-work of spin-polarized density functional theory (spin-DFT). For the treating of the structural properties, the electronic exchange and correlation (XC) functional was defined by generalised gradient approximation (GGA), whereas both GGA and GGA + U approximations are applied to treat and to compare the electronic and magnetic properties (U is the Coulomb repulsion energy). It has been confirmed that the ferromagnetic (FM) state of this alloy is found the most stable phase; however, all the equilibrium lattice parameters such as; lattice constant (a0), bulk modulus (B0), and its first-pressure derivative (B′) are computed in all paramagnetic, ferromagnetic and anti-ferromagnetic phases. The calculations of electronic properties unveil the perfect half-metallic character in the tetragonal Zn0.50Ti0.50S system. The computed magnetic properties reveal that the total magnetic moment is mainly originated from the transition element (TM) of Ti. Moreover, we have found that the p-d hybridisation is the paramount responsible for the reduction of the magnetic moment of TM from its free space charge value and for the production of minor magnetic moments on the nonmagnetic Zn and S sites.

First principles study of the electronic and magnetic properties of Zn1-xCoxSe alloys

The spin-polarized density functional theory as implemented within self-consistent plane wave pseudopotential method is used to investigate the electronic and magnetic properties of ternary alloys Zn1−xCoxSe (for x = 0.125, 0.25 and 0.375) in zinc blende structure. The spin polarised energy band structures reveals that the Zn1-xCoxSe is semiconducting ferromagnet for x = 0.125 and 0.25, it becomes HM ferromagnet for x = 0.375. The band gaps for x = 0.125 and 0.25 configurations are 1.09 and 1.07 eV for spin up channel and 0.65 and 0.39 for spin down channel respectively. The band gaps for x = 0.375 configuration is 0.18 eV for spin up channel. The magnetic moments for x = 0.125 and 0.25 configurations are 3.09 and 3.0 μB and for x = 0.375 configuration is 2.97 μB. The p-d hybridization reduces the local magnetic moment of Co atom from its free space charge value and induced the small atomic magnetic moment on Zn and Se atoms.

First principle calculations of electronic and magnetic properties of Mn-doped CdS (zinc blende): a theoretical study

AbstractThe electronic structure and magnetic properties of Mn doped zinc blende cadmium sulfide Cd1-xMnxS (x = 6.25 %) have been studied using spin-polarized density functional theory within the framework of Generalized Gradient Approximation (GGA), its further corrections including Hubbard U interactions (GGA + U) and a model for exchange and correlation potential Tran Blaha modified Becke-Johnson (TB-mBJ). Ferromagnetic interactions have been observed between Mn atoms via S atom due to strong p-d hybridization. The magnetic moments on Mn and its neighboring atoms have also been studied in detail using different charge analysis techniques. It has been observed that p-d hybridization reduced the value of local magnetic moment of Mn in comparison to its free space charge value and produced small local magnetic moments on the nonmagnetic S and Cd host sites. The magnetocrystalline anisotropy in [1 0 0] and [1 1 1] directions as well as exchange splitting parameters Noα and Noβ have been analyzed to confirm that ferromagnetism exists. We conclude that the ferromagnetic phase in Mn-doped CdS is not stable in “near” configuration but it is stable for “far” configuration. Mn doped CdS is a p-type semiconductor and the d-states at the top of the valence band edge give a very useful material for photoluminescence and magneto-optical devices.

Electronic and magnetic properties of Zn1−xFexSe alloys

The spin polarized density functional theory along with self consistent plane wave pseudopotential method is used to investigate electronic and magnetic properties of ternary Zn1−xFexSe alloys with x = 0.125, 0.25, 0.5 and 0.75. The exchange-correlation potential treated within generalized gradient approximation is used. The calculated spin-polarized band structures, partial and total density of states reveal that Zn0.875Fe0.125Se and Zn0.75Fe0.25Se exhibit half metallic ferromagnetic characteristics and Zn0.50Fe0.50Se is nearly half metallic in nature. The half metallic band gaps for x = 0.125 and 0.25 are 0.69 and 0.39eV respectively, while the corresponding band gaps are 0.86 and 0.81eV. The p-d hybridization reduces the magnetic moment of Fe atoms from its free space charge value of 4 μB and induces the small magnetic moments on Zn and Se sites. The results are compared with available experimental data.

First principles study of structural, electronic, magnetic and elastic properties of Mg0.75TM0.25S (TM=Mn, Fe, Co, Ni)

The objective of this work is to predict the structural, electronic, magnetic and elastic properties of Mg1−xTMxS (TM=Mn, Fe, Co and Ni) compound in the zinc blende Ferromagnetic phase using first principal approach. The structural and elastic properties are performed using the generalized gradient approximation proposed by Wu and Cohen(WC-GGA). However, the electronic and magnetic properties have been performed using modified Becke-Johnson potential combined with the LDA correlation (mBJLDA). The results show that all compounds Mg1−xMnxS, Mg1−xFexS and Mg1−xNixS exhibit a half-metallic ferromagnetic character with 100% spin-polarization at the Fermi level, except Mg1−xCoxS is a metal. For each compounds study here, the total magnetic momentum is an integer equal to magnetic moments of TM atom in their free space charge value. Due to the p–d hybridization, there is a small local magnetic moment on the Mg and S sites; whereas, the local magnetic moments of TM atom reduce from their free space charge value. In addition, we investigate the mechanical behavior of MgS and Mg1−xTMxS; all compounds studied here are mechanically stable and exhibit a strong anisotropic behavior.

First-Principles Study of Structural, Electronic and Magnetic Properties of Cr-Doped MgS

The objective of this work is to predict the structural, electronic and magnetic properties of Mg 1−xCr xS (x = 0, 0.25, 0.50, 0.75 and 1) compound in the zinc blende ferromagnetic phase using the first principal approach. The structural properties are performed using the generalized gradient approximation developed by Perdew–Burk–Ernzerhof (PBE-GGA). However, the electronic and magnetic properties have been performed using the modified Becke–Johnson potential combined with the LDA correlation (mBJLDA) which provides better description of electronic properties than PBE-GGA. The results show that this compound exhibits a half-metallic ferromagnetic character with 100 % spin polarization at the Fermi level. For all Cr concentrations (0.25, 0.50, 0.75 and 1), the total magnetic momentum is equal to 4 μB, and there is a small local magnetic moment on the Mg and S sites. Furthermore the local magnetic moments of Cr atom reduce from their free space charge value.

Study of Half-Metallic Ferromagnetism in Be0.75Ti0.25Y (Y = S, Se, and Te) Using Ab Initio Calculations: Potential Candidate for Spintronic Devices

The structural, elastic, electronic, and magnetic properties of Be0.75Ti0.25Y (Y = S, Se, and Te) have been investigated to understand their potential applications in spintonic devices. Crystals of BeS, BeSe, and BeTe, individually doped with Ti with a dopant concentration of x = 0.25, have been evaluated by using full-potential linearized augmented plane-wave plus local orbital method within the framework of density functional theory. We employed the Wu–Cohen generalized gradient approximation for optimizing the crystal structure and evaluating elastic properties. In order improve bandgap values and optical parameters, the modified Becke and Johnson (mBJ) potential has been employed. The theoretical investigation of band structure and density of states confirms the half-metallic ferromagnetic nature of these compounds. The elastic constants are calculated by the charpin method which shows that the compounds under consideration are brittle and anisotropic. Moreover, it is noted that tetrahedral crystal field splits the 3d state of Ti into triple degenerate t2g and double degenerate eg states. The exchange splitting energies Δx(d) and Δx(pd) and exchange constants (N0α) and (N0β) are predicted from triple degenerate t2g states, and negative values of N0β justify that the nature of effective potential is more attractive in spin down case rather than that in the spin up case. We also find the crystal field splitting (ΔEcrystal = Et2g−Eeg) energy and reduction of the local magnetic moment of Ti from its free space charge value and creation of small local magnetic moments on the non-magnetic Be, S, Se, and Te sites by p–d hybridization.

Electronic structure, magnetic and optical properties of Cr-doped GaAs using hybrid density functional

First-principles calculations based on the HSE hybrid density functional theory has been performed on the electronic structures, magnetic and optical properties of perfect GaAs and Cr-doped GaAs. The optical properties, including the complex dielectric function, optical reflectivity, extinction coefficient, refractive index, absorption coefficient and electron energy loss were discussed for radiation up to 20eV together with the calculated electronic structure. The results predicate that the system of Cr-doped GaAs exhibits typical half-metallic properties, in which Cr forms deep levels in the forbidden band and reduces the energy gap, increases static dielectric constant, and obviously red-shifts the absorption edge. In addition, a p-d hybridization reduces the magnetic moment of Cr from its free space charge value of 3μB and a smaller atomic magnetic moments of As and Ga atoms are generated.

The electronic and the magnetic properties of Mn doped wurtzite CdS: First-principles calculations

The electronic, structural and magnetic properties of Mn doped cadmium sulfide Cd1−xMnxS (x=6.25% and x=3.125%) are studied using spin-polarized density functional theory, in the framework of Local Density Approximation (LDA), Generalized Gradient Approximation (GGA), their extensions via on-site Hubbard U interactions and Tran Blaha modified Becke–Johnson (TB-mBJ) model potential. The Ferromagnetic interactions are studied between two Mn atoms via S atom due to strong p–d hybridization and d–d interactions. The ferromagnetic (FM) and anti-ferromagnetic (AFM) coupling properties between these atoms are studied with and without sulfur vacancies. The magnetic moments on Cd, S and Mn-atom are studied in detail by using different charge analysis techniques. The p–d hybridization reduces the local magnetic moment on Mn from its free space charge value and produces small local magnetic moments on the nonmagnetic Cd and S host sites. Mn doped CdS provides p-type semiconductor with d-states at top of the valence band edge, these states are responsible for a very useful luminescent and magneto-optical Mn:CdS material.

Structural, electronic and magnetic properties of Cd1–xTMxS (TM=Co and V) by ab-initio calculations

The structural, electronic and ferromagnetic properties of Cd1−xTMxS (TM=Co and V) compounds at x=0.25, 0.50 and 0.75 in zinc blende (B3) phase, have been investigated using all-electron full-potential linear muffin tin orbital (FP-LMTO) calculations within the frame work of the density functional theory and the generalized gradient approximation. The electronic properties exhibit half-metallic behavior at x=0.25, 0.50, and 0.75 for Cd1–xVxS and x=0.25 and 0.50 for Cd1−xCoxS, while Cd1−xCoxS with x=0.75 is nearly half-metallic. The calculated magnetic moment per substituted transition metal (TM) atom for half-metallic compounds is found to be 3µB, whereas that of a nearly half-metallic compound is 2.29µB. The analysis of band structure and density of states shows that the TM-3d states play a key role in generating spin-polarization and magnetic moment in these compounds. Furthermore, we establish that the p–d hybridization reduces the local magnetic moment of Co and enhances that of V from their free space charge value of 3µB and creates small local magnetic moments on nonmagnetic Cd and S sites. The exchange constant N0α and N0β have been calculated to validate the effects resulting from exchange splitting process.

Density functional theories study on the properties of Ga1−xCrxAs

Abstract The structural, electronic, magnetic and optical properties of Ga 1 − x Cr x As (x = 0, 6.25%, 12.5%) have been studied by first-principles calculations based on the HSE hybrid density functional theories. The optical properties, including the complex dielectric function, optical refractive index, extinction coefficient and absorption coefficient are discussed for radiation up to 15 eV. The results predicate that the system of Ga 1 − x Cr x As exhibits typical half-metallic properties, in which Cr forms deep levels in the forbidden band and reduces the energy gap, increases static dielectric constant and obviously red-shifts the absorption edge. With the increase of the fraction of Cr, the material gradually exhibits noticeable anisotropy in the photon energy range of 0–5 eV. In addition, the p-d hybridization reduces the magnetic moment of Cr from its free space charge value of 3 μ B and a smaller atomic magnetic moments of As and Ga atoms are generated.

First-principles study of the electronic and the magnetic properties of Cr-doped wurtzite cadmium sulfide (Cd1−x Cr x S, x = 12.5% and 6.25%)

The electronic and the magnetic properties of Cr-doped wurtzite cadmium sulfide (Cd1-xCrxS) at different concentrations (x = 12.5% and 6.25%) are investigated in the frame work of the generalized gradient approximation (GGA), its extension through on-site Hubbard U interactions (GGA+U), and the Tran Blaha modified Becke-Johnson (TB-mBJ) potential. The ferromagnetic exchange interactions between Cr-Cr atoms via S atoms are studied. The magnetic moments on these atoms are studied in detail by using different charge analysis techniques. The p-d hybridization reduces the local magnetic moment on Cr from its free space charge value and produces a small local magnetic moment on the nonmagnetic Cd and S host sites. Cr-doped CdS provides a half-metallic semiconductor.

The half-metallic ferromagnetism character in Be1−V Y (Y=Se and Te) alloys: An ab-initio study

Abstract Ab-initio calculations for V-doped BeSe and BeTe semiconductors are performed by means of all-electrons full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. The structural properties are optimized using the Wu-Cohen generalized gradient approximation functional, whereas modified Becke and Jhonson local density approximation functional has been employed for evaluating the spin-polarized electronic and magnetic properties. Magnetic stability at various doping concentrations in ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering is investigated by comparing the minimum total energies and enthalpies of formation (ΔH). Studied band structures, density of states, total energy, exchange interactions and magnetic moments manifest both alloys with half-metallic ferromagnetic behavior. Moreover, their valance bands are found to be paired ferromagnetically with V atoms. Furthermore, it was observed that the magnetic moment of vanadium atom reduces from free space charge value due to p–d hybridization which yields small magnetic moments on the Be, Se and Te sites.

Spin-polarized investigation of ferromagnetism on magnetic semiconductors MnxCa1−xS in the rock-salt phase

The structural, elastic, electronic and magnetic properties of the diluted magnetic semiconductors MnxCa1−xS in the rock-salt phase have been investigated using first-principles calculations with both LDA and LDA + U functional. Features such as lattice constant, bulk modulus, elastic constants, spin-polarized band structure, total and local densities of states have been computed. We predict the values of the exchange constants and the band edge spin splitting of the valence and conduction bands. The hybridization between S-3p and Mn-3d produces small local magnetic moment on the nonmagnetic Ca and S sites. The ferromagnetism is induced due to the exchange splitting of S-3p and Mn-3d hybridized bands. The total magnetic moment per Mn of MnxCa1−xS is 4.4μB and 4.5μB for LDA and LDA + U functional and is independent of the Mn concentration. The unfilled Mn-3d levels reduce the local magnetic moment of Mn from its free space charge value of 5μB–4.4μB and4.5μB for LDA and LDA + U functional due to 3p–3d hybridization.

First-principles investigations of structural, elastic, electronic and magnetic properties of Ga1−x Mn x P and In1−x Mn x P

We employ the full-potential linearized augmented plane wave plus local orbital (FP L/APW + lo) method based on the density functional theory (DFT) in order to investigate the structural, elastic, electronic, and magnetic properties of ordered dilute ferromagnetic semiconductors Ga1−x Mn x P and In1−x Mn x P at (x = 0.25) in the zinc blende phase, using generalized gradient approximation, GGA (PBE). To our knowledge the elastic constants of these compounds have not yet been measured or calculated, hence our results serve as a first quantitative theoretical prediction for future study. Results of calculated electronic structures and magnetic properties reveal that both Ga0.75Mn0.25P and In0.75Mn0.25P have stable ferromagnetic ground state, and they are ideal half-metallic (HM) ferromagnetic at their equilibrium lattice constants. Also we show the nature of the bonding from the charge spin-densities calculations. The calculated total magnetic moments are 4.0 μB per unit cell for both Ga0.75Mn0.25P and In0.75Mn0.25P, which agree with the Slater–Pauling rule quite well, and we observe that p–d hybridization reduces the local magnetic moment of Mn from its free space charge value and produces smaller local magnetic moments on the nonmagnetic Ga, In and P sites. The values of N 0α and N 0β exchange constants confirm the magnetic nature of these compounds. From the robust half-metallicity of Ga0.75Mn0.25P and In0.75Mn0.25P as a function of lattice constant is also investigated.