Tailoring the electronic structure and magnetic properties of pyrochlore Co 2 Ti 1-x Ge x O 4: A GGA+U ab initio study

摘要: We report the electronic structure and magnetic properties of Co2Ti1-xGexO4(0 ≤ x 1) spinel by means first-principles methods density functional theory involving generalized gradient approximation (GGA) along with on-site Coulomb interaction (Ueff) in exchange-correlation energy functional. Special emphasis has been given to explore site occupancy Ge atoms lattice introducing cationic disorder parameter (y) which is done such a way that one can tailor Pyrochlore geometry determine electronic/magnetic quantitatively. For all compositions (x), system exhibits weak tetragonal distortion (c/a ≠ due non-degenerate dz2and dx2-y2states (egorbitals) B-site Co. observe large exchange splitting (ΔEX~ 9 eV) between up down spin bands t2gand egstates, respectively, tetrahedral octahedral Co+2(4A2(g)(F)) moderate crystal-field (ΔCF~ 4 Jahn-Teller (ΔJT~ 0.9 eV). These features indicate strong intra-atomic also responsible for alteration band-gap (1.7 eV Eg≤ 3.3 The (JBB~-4.8 meV, (x,y) = (0.25, 0)) Co2+dominates overall antiferromagnetic behavior 'x' as compared interactions JAA(~-2.2 JAB(~-1.8 0)). without any disorderness system, net ferrimagnetic moment (Δμ) remains constant, however, Δμ increases progressively imbalance Co spins A- B-sites (ΔμMAX~ -4.4μBfor 0.75 y 1.0).