PRESSURE EFFECT ON SPIN, ELECTRONIC, AND THERMAL TRANSPORT IN TERNARY INTERMETALLICS

Abstract

The field of materials science has advanced significantly with the inception of computational technologies. Currently, more materials are designed on computers than those grown in laboratories. Designing and studying different aspects of a material using a computer helps us decide whether the material should be grown in laboratories. This process helps decrease lab waste and speeds up the discovery of novel materials. Using a computer, we can predict the possibility of synthesis and various properties of materials under varying external conditions. This thesis focuses on the computational investigation of structural, electronic, magnetic, topological, spin and current transport, and thermoelectric transport properties of ternary intermetallic compounds under strain and pressure conditions. We selected compounds from three different crystal classes for a thorough understanding of the effect of pressure on various properties. The materials that we studied are half-Heusler CoFeGe, hexagonal SrAgP, and tetragonal quasi two-dimensional KMgSb. The CoFeGe is studied for spin and current transport, SrAgP for topological and thermoelectric transport, and van der Waals KMgSb for thermal and electronic transport properties. These studies are presented in three different chapters. CoFeGe: Spintronics is an emerging form of electronics based on the electrons’ spin degree of freedom for which materials with robust half-metallic ferromagnet character are very attractive. Here, we determine the structural stability, electronic, magnetic, and mechanical properties of the half-Heusler (hH) compound CoFeGe, in particular in its cubic form. The first-principles calculations suggest that the electronic structure is robust with 100% spin polarization at the Fermi level under hydrostatic pressure and uni-axial strain. Both the longitudinal and Hall current polarization are calculated and the longitudinal current polarization (PL) is found to be > 99% and extremely robust under uniform pressure and uni-axial strain. The anomalous Hall conductivity and spin Hall conductivity of hH cubic CoFeGe (c-CoFeGe) are found to be ∼ −100 S/cm and ∼ 39 ¯h/e S/cm, respectively. Moreover, the Curie temperature of the alloy is calculated to be ∼ 524 K with a 3 μB magnetic moment. Lastly, the calculated mechanical properties indicate that c-CoFeGe is ductile and mechanically stable with a bulk modulus of ≈154 GPa. Overall, this analysis reveals that cubic CoFeGe is a robust half-metallic ferromagnet and an interesting material for spintronics applications.