Evaluating prospects for new transition-metal-rich and lanthanide-free permanent magnets, we calc... more Evaluating prospects for new transition-metal-rich and lanthanide-free permanent magnets, we calculate the magnetocrystalline anisotropy of dilute Co 1Àx Pt x and Co 1Àx Pd x alloys. The ab initio calculations are done by using the full-potential linear augmented plane wave method, treating exchange and correlation within the generalized gradient approximation. The anisotropy contributions, 11.9 kJ/m 3 per at. % Pd and 10.8 kJ/m 3 per at. % Pt, are in a range suitable for permanent magnets application. V
In this paper, we report the energy bands, density of states and the first ever Compton profiles ... more In this paper, we report the energy bands, density of states and the first ever Compton profiles of PbS and PbSe computed in the framework of spin-polarised relativistic Korringa-Kohn-Rostoker and ab initio pseudopotential with Hartree-Fock and density functional theory schemes. In addition, we have computed the energy bands and density of states using full-potential linearised augmented plane wave method. To compare our theoretical data, we have also measured the first ever isotropic Compton profiles at an intermediate resolution using our 740 GBq (20 Ci) 137 Cs Compton spectrometer. The Compton profiles scaled on equal-valence-electron-density show that PbSe is more covalent than PbS, which is in agreement with the present Mulliken's population data.
We study, by density functional and large-scale tight-binding transport calculations, the electro... more We study, by density functional and large-scale tight-binding transport calculations, the electronic structure, magnetism and transport properties of the recently proposed graphene ribbons with edges rolled to form nanotubes. Edges with armchair nanotubes present magnetic moments localized either in the tube or the ribbon and of metallic or half-metallic character, depending on the symmetry of the junction. These properties have potential for spin valve and spin filter devices with advantages over other proposed systems. Edges with zigzag nanotubes are either metallic or semiconducting without affecting the intrinsic mobility of the ribbon. Varying the type and size of the nanotubes and ribbons offers the possibility to tailor the magnetic and transport properties, making these systems very promising for applications.
Density-functional calculations are used to determine the electronic structure and magnetic prope... more Density-functional calculations are used to determine the electronic structure and magnetic properties of dilute magnetic semiconductors with the composition X 1−x Mn x N (X = Al, Ga, In, x = 6.25% and 12.5%). Emphasis is on the interatomic exchange as a function of the Mn-Mn distance. Our superlattice calculations show that the Mn dopants are spin-polarized with a half-metallic band gap and a magnetic moment of 4 μ B per Mn atom at x = 6.25 and 12.5%. The Mn (3d) bands lie in the band gap but partially hybridize with valence band or N 2p electrons, depending on the group-III element and on the spin direction. To calculate the exchange interaction parameters J ij , we have used a Green-function approach. The interaction between Mn atoms extends over several interatomic interactions and is mediated by nitrogen (2p) electrons. The exchange is always ferromagnetic and largest for the first nearest neighbors, but substantial ferromagnetic interactions persist over Mn-Mn distances up to sixth nearest neighbors in the considered supercell.
First ever isotropic experimental Compton profiles of GeS and GeSe are presented. Moreover, we pr... more First ever isotropic experimental Compton profiles of GeS and GeSe are presented. Moreover, we present Compton profiles, energy bands and density of states (DOS) using Hartree-Fock, density functional and pseudopotential schemes. It is seen that the Hartree-Fock and density functional theories show a reasonable agreement with the experiment. The equal-valence-electron-density profiles show that GeS is more ionic than GeSe. We have also reported energy bands and DOS using full potential linearized augmented plane-wave method. r
In this paper, we report the first ever experimental Compton profile study of WS 2 and WSe 2 empl... more In this paper, we report the first ever experimental Compton profile study of WS 2 and WSe 2 employing 20 Ci 137 Cs Compton spectrometer. To interpret our experimental data, the electronic properties of these compounds have been determined by linear combination of atomic orbitals, full potential linearised augmented plane-wave and spin polarised relativistic Korringa-Kohn-Rostoker (SPR-KKR) schemes. The band structure calculations show that both the WS 2 and WSe 2 are indirect-gap semiconductors. The SPR-KKR calculations are found to be relatively in poor agreement with the experimental electron momentum densities. The relative nature of bonding in both the dichalcogenides is explained in terms of equalvalence-electron-density profiles, Mulliken's population and valence band charge densities.
... An unusual small band gap and real space analysis of our first ever experimental Compton prof... more ... An unusual small band gap and real space analysis of our first ever experimental Compton profile are discussed. ... The small value of band gap is also explained with the help of real space analysis of our first ever experimental Compton profile. ...
The formation of magnetic moment due to the dopants with p-orbital (d-orbital) is named d 0 (d−) ... more The formation of magnetic moment due to the dopants with p-orbital (d-orbital) is named d 0 (d−) magnetism, where the ion without (with) partially filled d states is found to be responsible for the observed magnetic properties. To study the origin of magnetism at a fundamental electronic level in such materials, as a representative case, we theoretically investigate ferromagnetism in MgO doped with transition metal (Mn) and non-metal (C). The generalized gradient approximation based first-principles calculations are used to investigate substitutional doping of metal (Mn) and nonmetal (C), both with and without the presence of neighboring oxygen vacancy sites. Furthermore, the case of co-doping of (Mn, C) in MgO system is also investigated. It is observed that the oxygen vacancies do not play a role in tuning the ferromagnetism in presence of Mn dopants, but have a significant influence on total magnetism of the C doped system. In fact, we find that in MgO the d 0 magnetism through C doping is curtailed by pairing of the substitutional dopant with naturally occurring O vacancies. On the other hand, in case of (Mn, C) co-doped MgO the strong hybridization between the C (2 p) and the Mn(3d) states suggests that co-doping is a promising approach to enhance the ferromagnetic coupling between the nearestneighboring dopant and host atoms. Therefore, (Mn,C) co-doped MgO is expected to be a ferromagnetic semiconductor with long ranged ferromagnetism and high Curie temperature.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2007
The Compton profiles of Rh along [1 0 0] and [1 1 0] directions are measured using 100 mCi 241 Am... more The Compton profiles of Rh along [1 0 0] and [1 1 0] directions are measured using 100 mCi 241 Am Compton spectrometer. To compare the experimental data, we have computed the Compton profiles and energy bands using spin-polarised relativistic Korringa-Kohn-Rostoker (SPR-KKR) and density functional theory schemes. The experimental and theoretical data are also compared with the available augmented plane wave and linear combination of Gaussian orbitals calculations. The origin of anisotropy in the momentum densities is discussed in terms of the energy bands and the Fermi surface topology. Among the various model calculations, it is seen that the KKR calculations are in better agreement with the absolute profiles but they significantly overestimate the anisotropy in momentum densities.
... aemail: gulzar_ahmed61@yahoo.com, bemail: blahuja@yahoo.com, cemail: nlheda@yahoo. com demail... more ... aemail: gulzar_ahmed61@yahoo.com, bemail: blahuja@yahoo.com, cemail: nlheda@yahoo. com demail: vinit.sharma.mlsu@gmail.com, eemail: ashish.82physics ... BK Sharma, S. Mathur, NL Heda, M. Itou, A. Andrejczuk, Y.Sakurai, A. Chakrabarti, S. Banik, AM Awasthi and SR ...
Ab-initio methods have been employed to investigate the electronic and elastic properties of bery... more Ab-initio methods have been employed to investigate the electronic and elastic properties of beryllium chalcogenides (namely BeS, BeSe and BeTe). The electron momentum density, autocorrelation function and energy band gap have been computed using the linear combination of atomic orbitals method. Using the full potential linearized augmented plane-wave and projector-augmented wave methods, the energy bands and density of states (DOS) along with elastic properties are also calculated. The electronic band structure, total and partial DOS and elastic moduli obtained from the present calculations are found to be in good agreement with available earlier data. The calculated valence band width, equal valence electron density curve and bulk modulus confirm the trend of ionicity BeS>BeSe>BeTe.
... Permissions & Reprints. Electronic structure, Compton profiles and cohesive prope... more ... Permissions & Reprints. Electronic structure, Compton profiles and cohesive properties of Cs-halides. Vinit Sharma a , Shailja Tiwari a and BL Ahuja Corresponding Author Contact Information , a , E-mail The Corresponding Author. ... View Within Article. 4.2. Compton profiles. ...
We present the first ever Compton scattering study on W x Cu 1−x (x = 0.60, 0.72) alloys. The Com... more We present the first ever Compton scattering study on W x Cu 1−x (x = 0.60, 0.72) alloys. The Compton profile measurements have been made using 20 Ci 137 Cs ␥-ray source. The experimental data are compared with the superposition of APW-based Compton profiles of constituent metals. A schematic study on charge transfer has been reported using the experimental valence band Compton profiles of both the alloys, W and Cu. Our first ever data support the charge transfer from W to Cu on alloying, which is also confirmed by our band structure calculations employing exact muffin-tin orbitals method (EMTO).
The electron momentum density distribution in intermetallic TiCu is measured and compared with ca... more The electron momentum density distribution in intermetallic TiCu is measured and compared with calculations based on linear combination of atomic orbitals (LCAO) and spin polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) methods. The spherically averaged theoretical Compton profiles are in good agreement with the measurement. The better agreement is, however, shown by the SPR-KKR method. To investigate the bonding mechanism in the alloy, the density of states has also been determined from SPR-KKR method.
Evaluating prospects for new transition-metal-rich and lanthanide-free permanent magnets, we calc... more Evaluating prospects for new transition-metal-rich and lanthanide-free permanent magnets, we calculate the magnetocrystalline anisotropy of dilute Co 1Àx Pt x and Co 1Àx Pd x alloys. The ab initio calculations are done by using the full-potential linear augmented plane wave method, treating exchange and correlation within the generalized gradient approximation. The anisotropy contributions, 11.9 kJ/m 3 per at. % Pd and 10.8 kJ/m 3 per at. % Pt, are in a range suitable for permanent magnets application. V
In this paper, we report the energy bands, density of states and the first ever Compton profiles ... more In this paper, we report the energy bands, density of states and the first ever Compton profiles of PbS and PbSe computed in the framework of spin-polarised relativistic Korringa-Kohn-Rostoker and ab initio pseudopotential with Hartree-Fock and density functional theory schemes. In addition, we have computed the energy bands and density of states using full-potential linearised augmented plane wave method. To compare our theoretical data, we have also measured the first ever isotropic Compton profiles at an intermediate resolution using our 740 GBq (20 Ci) 137 Cs Compton spectrometer. The Compton profiles scaled on equal-valence-electron-density show that PbSe is more covalent than PbS, which is in agreement with the present Mulliken's population data.
We study, by density functional and large-scale tight-binding transport calculations, the electro... more We study, by density functional and large-scale tight-binding transport calculations, the electronic structure, magnetism and transport properties of the recently proposed graphene ribbons with edges rolled to form nanotubes. Edges with armchair nanotubes present magnetic moments localized either in the tube or the ribbon and of metallic or half-metallic character, depending on the symmetry of the junction. These properties have potential for spin valve and spin filter devices with advantages over other proposed systems. Edges with zigzag nanotubes are either metallic or semiconducting without affecting the intrinsic mobility of the ribbon. Varying the type and size of the nanotubes and ribbons offers the possibility to tailor the magnetic and transport properties, making these systems very promising for applications.
Density-functional calculations are used to determine the electronic structure and magnetic prope... more Density-functional calculations are used to determine the electronic structure and magnetic properties of dilute magnetic semiconductors with the composition X 1−x Mn x N (X = Al, Ga, In, x = 6.25% and 12.5%). Emphasis is on the interatomic exchange as a function of the Mn-Mn distance. Our superlattice calculations show that the Mn dopants are spin-polarized with a half-metallic band gap and a magnetic moment of 4 μ B per Mn atom at x = 6.25 and 12.5%. The Mn (3d) bands lie in the band gap but partially hybridize with valence band or N 2p electrons, depending on the group-III element and on the spin direction. To calculate the exchange interaction parameters J ij , we have used a Green-function approach. The interaction between Mn atoms extends over several interatomic interactions and is mediated by nitrogen (2p) electrons. The exchange is always ferromagnetic and largest for the first nearest neighbors, but substantial ferromagnetic interactions persist over Mn-Mn distances up to sixth nearest neighbors in the considered supercell.
First ever isotropic experimental Compton profiles of GeS and GeSe are presented. Moreover, we pr... more First ever isotropic experimental Compton profiles of GeS and GeSe are presented. Moreover, we present Compton profiles, energy bands and density of states (DOS) using Hartree-Fock, density functional and pseudopotential schemes. It is seen that the Hartree-Fock and density functional theories show a reasonable agreement with the experiment. The equal-valence-electron-density profiles show that GeS is more ionic than GeSe. We have also reported energy bands and DOS using full potential linearized augmented plane-wave method. r
In this paper, we report the first ever experimental Compton profile study of WS 2 and WSe 2 empl... more In this paper, we report the first ever experimental Compton profile study of WS 2 and WSe 2 employing 20 Ci 137 Cs Compton spectrometer. To interpret our experimental data, the electronic properties of these compounds have been determined by linear combination of atomic orbitals, full potential linearised augmented plane-wave and spin polarised relativistic Korringa-Kohn-Rostoker (SPR-KKR) schemes. The band structure calculations show that both the WS 2 and WSe 2 are indirect-gap semiconductors. The SPR-KKR calculations are found to be relatively in poor agreement with the experimental electron momentum densities. The relative nature of bonding in both the dichalcogenides is explained in terms of equalvalence-electron-density profiles, Mulliken's population and valence band charge densities.
... An unusual small band gap and real space analysis of our first ever experimental Compton prof... more ... An unusual small band gap and real space analysis of our first ever experimental Compton profile are discussed. ... The small value of band gap is also explained with the help of real space analysis of our first ever experimental Compton profile. ...
The formation of magnetic moment due to the dopants with p-orbital (d-orbital) is named d 0 (d−) ... more The formation of magnetic moment due to the dopants with p-orbital (d-orbital) is named d 0 (d−) magnetism, where the ion without (with) partially filled d states is found to be responsible for the observed magnetic properties. To study the origin of magnetism at a fundamental electronic level in such materials, as a representative case, we theoretically investigate ferromagnetism in MgO doped with transition metal (Mn) and non-metal (C). The generalized gradient approximation based first-principles calculations are used to investigate substitutional doping of metal (Mn) and nonmetal (C), both with and without the presence of neighboring oxygen vacancy sites. Furthermore, the case of co-doping of (Mn, C) in MgO system is also investigated. It is observed that the oxygen vacancies do not play a role in tuning the ferromagnetism in presence of Mn dopants, but have a significant influence on total magnetism of the C doped system. In fact, we find that in MgO the d 0 magnetism through C doping is curtailed by pairing of the substitutional dopant with naturally occurring O vacancies. On the other hand, in case of (Mn, C) co-doped MgO the strong hybridization between the C (2 p) and the Mn(3d) states suggests that co-doping is a promising approach to enhance the ferromagnetic coupling between the nearestneighboring dopant and host atoms. Therefore, (Mn,C) co-doped MgO is expected to be a ferromagnetic semiconductor with long ranged ferromagnetism and high Curie temperature.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2007
The Compton profiles of Rh along [1 0 0] and [1 1 0] directions are measured using 100 mCi 241 Am... more The Compton profiles of Rh along [1 0 0] and [1 1 0] directions are measured using 100 mCi 241 Am Compton spectrometer. To compare the experimental data, we have computed the Compton profiles and energy bands using spin-polarised relativistic Korringa-Kohn-Rostoker (SPR-KKR) and density functional theory schemes. The experimental and theoretical data are also compared with the available augmented plane wave and linear combination of Gaussian orbitals calculations. The origin of anisotropy in the momentum densities is discussed in terms of the energy bands and the Fermi surface topology. Among the various model calculations, it is seen that the KKR calculations are in better agreement with the absolute profiles but they significantly overestimate the anisotropy in momentum densities.
... aemail: gulzar_ahmed61@yahoo.com, bemail: blahuja@yahoo.com, cemail: nlheda@yahoo. com demail... more ... aemail: gulzar_ahmed61@yahoo.com, bemail: blahuja@yahoo.com, cemail: nlheda@yahoo. com demail: vinit.sharma.mlsu@gmail.com, eemail: ashish.82physics ... BK Sharma, S. Mathur, NL Heda, M. Itou, A. Andrejczuk, Y.Sakurai, A. Chakrabarti, S. Banik, AM Awasthi and SR ...
Ab-initio methods have been employed to investigate the electronic and elastic properties of bery... more Ab-initio methods have been employed to investigate the electronic and elastic properties of beryllium chalcogenides (namely BeS, BeSe and BeTe). The electron momentum density, autocorrelation function and energy band gap have been computed using the linear combination of atomic orbitals method. Using the full potential linearized augmented plane-wave and projector-augmented wave methods, the energy bands and density of states (DOS) along with elastic properties are also calculated. The electronic band structure, total and partial DOS and elastic moduli obtained from the present calculations are found to be in good agreement with available earlier data. The calculated valence band width, equal valence electron density curve and bulk modulus confirm the trend of ionicity BeS>BeSe>BeTe.
... Permissions & Reprints. Electronic structure, Compton profiles and cohesive prope... more ... Permissions & Reprints. Electronic structure, Compton profiles and cohesive properties of Cs-halides. Vinit Sharma a , Shailja Tiwari a and BL Ahuja Corresponding Author Contact Information , a , E-mail The Corresponding Author. ... View Within Article. 4.2. Compton profiles. ...
We present the first ever Compton scattering study on W x Cu 1−x (x = 0.60, 0.72) alloys. The Com... more We present the first ever Compton scattering study on W x Cu 1−x (x = 0.60, 0.72) alloys. The Compton profile measurements have been made using 20 Ci 137 Cs ␥-ray source. The experimental data are compared with the superposition of APW-based Compton profiles of constituent metals. A schematic study on charge transfer has been reported using the experimental valence band Compton profiles of both the alloys, W and Cu. Our first ever data support the charge transfer from W to Cu on alloying, which is also confirmed by our band structure calculations employing exact muffin-tin orbitals method (EMTO).
The electron momentum density distribution in intermetallic TiCu is measured and compared with ca... more The electron momentum density distribution in intermetallic TiCu is measured and compared with calculations based on linear combination of atomic orbitals (LCAO) and spin polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) methods. The spherically averaged theoretical Compton profiles are in good agreement with the measurement. The better agreement is, however, shown by the SPR-KKR method. To investigate the bonding mechanism in the alloy, the density of states has also been determined from SPR-KKR method.
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