R. K. Thapa

Study of electronic and magnetic properties in 4f electron based cubic EuAlO3: a first-principles calculation

The electronic and magnetic properties of EuAlO3 are calculated by first-principles full-potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). The exchange and correlation potential is treated with different approximations: mBJ and GGA + U. Coulomb repulsion (U) has been calculated using super-cell calculations for EuAlO3. The GGA + U calculations reveal an indirect band gap of 4.6 eV for EuAlO3 in the spin down channel supporting the half metallic (HM) nature of the system. An effective integral magnetic moment also supported the HM nature of EuAlO3.

A SIMPLE THEORY OF PHOTOFIELD EMISSION FROM THE SURFACE OF A METAL

A simple model calculation of photofield emission is presented in which the photofield emission current (PFEC) is calculated for metal W. The matrix element for photoexcitation is evaluated by using the free electron wavefunction. The transmission probability D(W) is deduced by solving Airys differential equation. The variation of PFEC is studied as a function of parameters like the applied high electric field, the photon energy, the initial state energy with reference to the Fermi level. It is found that in addition to D(W), the matrix element Mfi also has effect on the photofield emission.

An ab initio study of filled skutterudites ROs4P12 (R = Sm, Eu and Gd)

The elastic, electronic, magnetic and optical properties of filled skutterudite ROs4P12 (R = Sm, Eu and Gd) have been studied by first principles calculation. The full-potential linearized augmented plane wave method based on density functional theory was employed. For the exchange-correlation potential, local spin density approximation + Coulomb repulsion (LSDA + U) is used to treat the f-electrons more effectively. The numerical values of the elastic parameters are estimated in the framework of the Voigt–Reuss–Hill approximation. OsP-based filled skutterudite with localized 4f and 5d-electrons shows dense energy bands near Fermi energy originating from rare earth and Os atoms. The dense density of states near EF reveals that these compounds are suitable for thermoelectric application. Optical constants including dielectric function, optical reflectivity and refractive index are calculated for photon energy radiation up to 12 eV. The exchange-splitting of R-4f states were analyzed to explain the ferromagnetic behavior of ROs4P12.

Structural, electronic, mechanical, and thermoelectric properties of a novel half Heusler compound HfPtPb

We explore the structural, electronic, mechanical, and thermoelectric properties of a new half Heusler compound HfPtPb, an all metallic heavy element, recently proposed to be stable [Gautier et al., Nat. Chem. 7, 308 (2015)]. In this work, we employ density functional theory and semi-classical Boltzmann transport equations with constant relaxation time approximation. The mechanical properties, such as shear modulus, Youngs modulus, elastic constants, Poissons ratio, and shear anisotropy factor, have been investigated. The elastic and phonon properties reveal that this compound is mechanically and dynamically stable. Pughs ratio and Frantsevichs ratio demonstrate its ductile behavior, and the shear anisotropic factor reveals the anisotropic nature of HfPtPb. The band structure predicts this compound to be a semiconductor with a band gap of 0.86 eV. The thermoelectric transport parameters, such as Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and lattice thermal conducti...

Electronic structure and x-ray spectroscopy of Cu2MnAl1–xGax

We explore the electronic and related properties of Cu2MnAl1–xGax with a first-principles, relativistic multiscattering Green function approach. We discuss our results in relation to existing experimental data and show that the electron-core hole interaction is essential for the description of the optical spectra especially in describing the X-ray absorption and magnetic circular dichroism spectra at the L2,3 edges of Cu and Mn.

Half metallic ferromagnetism in tri-layered perovskites Sr4T3O10(T = Co, Rh)

First-principles density functional theory (DFT) is used to investigate the electronic and magnetic properties of Sr4Rh3O10, a member of the Ruddlesden-Popper series. Based on the DFT calculations taking into account the co-operative effect of Coulomb interaction (U) and spin-orbit couplings (SOC), Sr4Rh3O10 is found to be a half metallic ferromagnet (HMF) with total magnetic moment μtot = 12 μB per unit cell. The material has almost 100% spin-polarization at the Fermi level despite of sizable SOC. Replacement of Rh atom by the isovalent Co atom is considered. Upon full-replacement of Co, a low-spin to intermediate spin transition happens resulting in a HMF state with the total magnetic moment three-time larger (i.e., μtot = 36 μB per unit cell), compared to Sr4Rh3O10. We propose Sr4Rh3O10 and Sr4Co3O10 as candidates of half metals.

Effect of Fe-Ru doping in the electronic and thermoelectric properties of new filled skutterudite Ba(Fe,Ru)4As12

We have performed the density functional theory based calculation to study the electronic and thermoelectric properties of BaFe4−xRuxAs12 (x = 0%, 25%, 50%, 75%, and 100%) within the framework of the full potential-linearized augmented plane wave method. The composite alloys are found to be stable in their optimized crystal structures and their lattice constants are in close agreement with the corresponding experimental reports. The structural stability and mechanical properties are also studied using their elastic constants. The hardness of these materials increases with increasing concentration of Ru, which also donates the covalent nature of inter-atomic bonding of BaRu4As12. The analysis of energy bands and density of states reflects the semi-metallic nature of BaFe4As12 and BaRu4As12, whereas other doped materials show metallic character. The electronic structure calculation suggests the high Seebeck coefficient with the efficient thermoelectric application of these materials. The thermal transport i...

Electronic and Magnetic Properties of Fe Atomic Chain and Fe Atomic Plane: An ab initio Study

The electronic and magnetic properties of Fe atomic wire and atomic plane have been theoretically investigated from full potential linearized augmented plane wave (FPLAPW) method within a frame work of density functional theory (DFT). This work is based on the comparative study of number of Fe nanochains with infinite length and infinitely spread Fe nanosheet. A most commonly adopted GGA approximation is used for electron exchange correlation. In our calculation, the property of Fe-chain is predicted to be magnetic metal with the presence of deep valley (in Spin-up DOS) and a peak (in Spin-down DOS) at Fermi level (EF) shows the antisymmetric DOS. The presence of antisymmetric DOS is a signature of exchange splitting between the degenerated d-states. The splitting between t2g states is very prominent in Fe-chain which enhances the magnetic moment. The magnetic moment decreases with the increase in number of Fe-chains.

A theoretical study of photofield emission in gallium arsenide

We have presented in this report the application of free electron potential model in the study photofield emission current (PFEC) in gallium arsenide (GaAs). The variation of photofield emission current is presented as a function of parameters like the applied high electric field, the photon energy, the initial state energy with reference to the Fermi level. Relation of change of PFEC to DOS is also shown for GaAs.

A theoretical study of Photofield emission in Gallium Arsenide using Kronig-Penney potential model

We have presented in this report the application of free electron potential model in the study photofield emission current (PFEC) in gallium arsenide (GaAs). The variation of photofield emission current is presented as a function of parameters like the applied high electric field, the photon energy, the initial state energy with reference to the Fermi level. Relation of change of PFEC to DOS is also shown for GaAs.