Papers by Author: B.L. Ahuja

Abstract: We have computed the Mulliken’s population (MP) to deduce charge transfer from WO in semiconducting WO3 using density functional theory (DFT) within pseudopotential scheme. In the DFT scheme, second order generalized gradient approximation for exchange and correlation has been implemented for the first time. The MP data show significant difference in charge transfer between W and six non–equivalent O atoms. In addition, the full potential linearized augmented plane wave method has been applied to compute the partial and total density of states. The MP data have also been explained in terms of partial DOS.

Abstract: Abstract. We report the Compton profiles of tantalum chalcogenides (TaS2 and TaSSe) using Hartree–Fock and hybridization of Hartree–Fock and density functional theories within linear combination of atomic (Gaussian) orbitals. To interpret the theoretical data on Compton line shapes, we have measured the Compton profiles using our in-house 100 mCi 241Am γ-ray Compton spectrometer. To understand the relative nature of bonding, we have obtained the equal-valence-electron-density (EVED) profiles. The EVED profiles shows that charge in TaSSe is more localized than TaS2 in the bonding direction which confirms that TaSSe is more covalent than TaS2, which is in agreement with the Mulliken’s population analysis.

Abstract: We report the first ever isotropic experimental Compton profile of tungsten ditelluride using 20 Ci ¹³⁷Cs Compton spectrometer. To compare our experimental data, we have also computed the Compton profiles, energy bands, density of states and band gap using Hartree-Fock and density functional theory within linear combination of atomic orbitals. The measured data is found to be in better accordance with the generalised gradient approximation of density functional theory than Hartree-Fock and local density approximation. We have discussed the nature of bonding in WTe₂ using energy bands and density of states.

Abstract: Spin momentum density in Ni₂Mn_1.4Sn_0.6 shape memory alloy has been measured using magnetic Compton scattering technique. The experiment has been performed using 182 keV circularly polarized synchrotron radiation at temperature 10 K at SPring-8, Japan. Experimental magnetic Compton profile has been decomposed to determine the site specific magnetic moments, where the magnetic moment at Mn site was found to be dominating. It is seen that the total spin moment in present non-stoichiometric alloy is smaller than that of stoichiometric Ni₂MnSn.

Abstract: We report a detailed investigation of the magneto-transport and magnetic properties of Mn excess Ni-Mn-Ga using the resistivity and magnetization measurements. Magnetoresistance (MR) has been measured in the ferromagnetic state for different compositions in the austenitic, premartensitic and martensitic phases. With Mn doping in Ni2-yMn1+yGa, a decrease in magnetization and MR has been found, since the doped Mn atoms in Ni position are in the antiferromagnetic configuration with the Mn atoms in Mn position. MR for the parent stoichiometric composition Ni2MnGa varies almost linearly with field in the austenitic and pre-martensitic phases, and shows a cusp-like shape in the martensitic phase. This has been explained by the changes in twin and domain structures in the martensitic phase. Hysteresis in the heating and cooling cycles is a characteristic of the first order nature of the martensitic phase transition.

Abstract: We present the first ever theoretical and experimental charge Compton profiles of Ni2MnGa Heusler alloy. The measurements have been made using magnetic Compton spectrometer at SPring8, Japan. The Compton profiles and energy bands have been computed using Hartree-Fock, density functional theory with local density and generalized gradient approximations. It is seen that the Hartree-Fock based Compton profile is relatively in better agreement with the experimental profiles. In addition, we also report the energy bands, density of states and valence charge densities using full potential linearized augmented plane-wave method.

Abstract: The Compton profile, projection of electron momentum density distribution along the scattering vector, is very sensitive to the behavior of valence electrons in a variety of materials. In this paper theoretical aspects related to measurement of spin momentum densities of magnetic materials using Compton scattering is reviewed. To highlight the potential of the magnetic Compton scattering, the spin momentum densities in Ni-Mn-Ga Heusler alloys at various temperatures and magnetic fields are presented. The magnetic Compton profiles are mainly analyzed in terms of the contribution from the 3d electrons of Mn. A comparison of the magnetic Compton data with other magnetization studies illustrates its importance in exploring the magnetic effects in ferro- or ferri-magnetic materials.