First-principles Study Of Electronic Properties And Magnetic Properties Of Transition Metal Oxides

Transition metal oxides constitute the basis for a large field of exotic physical phenomena,Many tremendous efforts have been devoted to exploring the novel magnetic and electronic properties of transition metal oxides.In this thesis,we investigated the electronic and magnetic properties of the tetragonal molybdenum phosphate MoOPO4 and the charge ordered phenomenon in ?-V2OPO4 within the monoclinic C2/c phase by means of first-principles calculations based on the density functional theory within the semilocal generalized gradient approximation that includes the Hubbard repulsion term to take into account the electronic correlationsConcerning the MoOPO4,our results demonstrated that the Neel ordering on the square lattice plane,experimentally observed,is indeed the magnetic ground state on conditions that the effective electronic correlation correction is smaller than 2.0 eV.Otherwise,the ferromagnetic alignment are established.In addition,the out-of-plane ferromagnetic interaction is well reproduced.The computed exchange constants,extracted from the classical Heisenberg model,show that the modest antiferromagnetic in-plane nearest-neighbor coupling play a decisive role in the stabilization of the Neel spin alignment,in conjunction with the remarkable ferromagnetic in-plane next nearest-neighbor interaction.In addition,the spin-orbit coupling of Mo 4d electron have been scrutinized by supplemental calculations,taking into account spin-orbit interactionAs for ?-V2OPO4 within the monoclinic C2/c phase,our results demonstrated that the AFM-?ordering,in which spin on all V2+atoms are parallel and so do the spin on all V3+atoms while these two spin sublattices are antiparallel to each other,experimentally observed,is the magnetic ground state,irrespective of whether the correlation was adopted or not.Alternatively,our theoretical results highlight the importance role of electronic correlation in reasonably reproducing the electronic properties of ?-V2OPO4,including the charge ordering,metal-insulator transition,spin orientation as well as structural distortion.Furthermore,the charge ordering scenario has been analyzed in details in terms of Bader charge,magnetic moments,volume difference and octahedron distortion index.In addition,the phase diagram has been established with respect to correlation strengths.