EFG and Magnetic Studies of Actinide-Post Transition Metals

Abstract

In this thesis, we explore the structural and magnetic properties as well as electric field gradient (EFG), hyperfine field (HFF) and quadrupole coupling constant in actinide digallides AcGa2 (Ac=U, Np, Pu), NpPx3 (Px =Al, In, Ga) and UX3 (X =In, Tl, Pb) by using local density approximation (LDA), generalized gradient approximation (GGA) with onsite Hubbard potentials LDA+U and GGA+U and Hybrid Wu-Cohen GGA (HF-WC). The hexagonal AB2 type AcGa2 and cubic AuCu3 type NpPx3 as well as UX3 compounds are optimized. The lattice constants, bulk moduli, optimized volumes and ground state energies of these compounds are evaluated from the optimized structures. Our results show that the calculated values of these structural parameters are consistent with the available experimental results. The magnetic structures of the materials under study are investigated by calculating the ferromagnetic, antiferromagnetic and non magnetic phase energies. The UGa2, NpGa2 and NpPx3 have lowest energies in ferromagnetic phase while PuGa2 and UX3 prefer in antiferromagnetic phase, which is in agreement with the experimental results. Due to the 5f- electronic states in these compounds spin orbit coupling (SOC) effect has been considered to include. The spin, orbital and total magnetic moment at U, Np and Pu sites have been calculated computationally with the presence and absence of SOC. Our calculated magnetic moments at uranium, neptunium and plutonium sites are consistent with the experimental values. The orbital, dipolar, Fermi contact as well as total hyperfine and its origin in actinide as well as post transition atomic sites have been investigated for the first time in these compounds. The EFG and quadrupole coupling constant of uranium, neptunium and plutonium atom have been calculated and discussed in detail. These properties are mainly originated from f- states at uranium sites while p- states at post transition sites.