Ab-initio Study Of Half-metallic Ferromagnetism Response In Transition Metal Doped Semiconductors

The discovery of half-metallic ferromagnets (HMFs) has offered an additional impetus to the development of spintronics in which electron spin is manipulated along with its charge to impart multi-functionalities in advance electronic devices. In this thesis, the ab-initio calculations are employed to examine the fundamental properties like structural, elastic, electronic and magnetic for vanadium (V)-doped WTe (W=Zn, Cd), V-doped XY (X=Be, Mg and Y=Se, Te) and manganese (Mn)-doped AlZ (Z=N, P and As) compounds at different doping concentrations. These calculations are based on density functional theory (DFT) that is the widely accepted and executed theoretical tools to analyze the ground-state (GS) physical properties of insulators, metals, semi-metals, semiconductors, half-metals and superconductors. Within DFT, we utilized the full potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method.To compute the structural properties, the total energy in minimized as a function of the unit cell volume with the help of Wu-Cohen generalized gradient approximation (WC-GGA). During this structural optimization, the equilibrium lattice parameters (ao) and bulk moduli,(Bo) are estimated. While evaluating elastic properties, the elastic constants are determined to explore the significant information regarding stability, stiffness, elasticity and nature of the operating forces in solids. The electronic properties, including electronic band structures, total and partial density of states (TDOS and PDOS) and charge densities are computed with modified Becke and Johnson local density approximation (mBJLDA) by using the equilibrium lattice parameters. In addition to mBJLDA, WC-GGA is also used to analyze these properties only for Cd1-xVxTe (0≤x≤1) and the comparison of their results with previous experimental and theoretical studies reveals the significantly improved performance of the former DFT potential. The electronic band structures show that the investigated compounds are metallic in one spin direction (spin-up in our study) whereas the Fermi level (EF) resides in the band gap between valence band (VB) and conduction band (CB) making them behave as semiconductors. Such character of the studied compounds confirms their HM nature. For clear understanding of half-metallicity in these compounds, an important electronic structure parameter, the HM gap (EHM) is also computed. To analyze electronic band structures in details, the TDOS along with PDOS are also worked out. These results reveal formation of a spin-polarized impurity band due to strong pd hybridization between Y/Z p-states and transition metals (TMs) d-states. The unfilled TMs (V and Mn) d orbitals are responsible of spin exchange splitting (△x(d) and△x(pd)) and total magnetic moments in our compounds. In exchange splitting process, the CB and VB contributions are viewed by determining the exchange constants (N0α and N0β). The pd hybridization not only reduces the atomic magnetic moment of V/Mn from3μB/4μB (μB is the Bohr magneton) but also generates small atomic magnetic moments on the non-magnetic (NM) sites. To explore the bonding nature of W/X/Al-Y/Z and V/Mn-Y/Z bonds and the bonding properties of the investigated compounds, we have plotted spin charge densities for both spins. The electronegativity difference between cation and anion decides the bonding charge displacement between them. Finally, we studied the variation of half-metallicity by increasing pressure (reducing lattice parameter from its GS value) for potential and useful applications of the considered materials in spintronic. Our study has introduced theoretically novel HMFs to make their practical use in spintronic devices.