Theoretical Study Of P-d Hybridization In Co Perovskite

The studies of perovskite manganese oxides have attracted much renewed attention since the discovery of colossal magnetoresistance (CMR) effect in the mid-1990s, because CMR effects are great valuable in industrial demand, such as the magnetic memory,magnetic random access memories,magnetic sensors, As a fundamental physics research,the manganite system exhibits many intriguing physical behaviors; e.g. paramagnetic-ferromagnetic phase transition together with insulator-metal transition,charge-orbital ordering,phase separation,Jahn-Teller distortion,double exchange model and the coupling between them; especially,the investigation will have important significance for the spintronic application. The intensive study is focus on the structure of all kinds of ordings and their effects on the electronic and magnetic properties, as well as the origin of phase separation and its relationship to the colossal magnetoresistance, our study is focus on the p-d hybridization in perovskite compound, and its effect to the magnetic state. The main contents in the dissertation are presented as follow:In chapter 1, we make a brief introduction to the research history, the crystal structure and lattice distortion, the essential physical mechanism such as double exchange interaction, the Jahn-Teller effect and the super exchange interaction, the charge ordering and its effect on the electronic and magnetic properties as well as its stabilization.In chapter 2, we apply the multiband Hubbard model to describe the realistic perovskite, that is, take the degeneracy of d and p orbitals, and on-site Coulomb and exchange interaction. Within the unrestricted Hartree-Fock approximation, we linearize the Hamiltonian. Meanwhile, we use the real space recursion method to calculate the electronic of the different magnetic states. We obtain the possible magnetic structure and its properities of the system.In chapter 3, the real-space recursion method and unrestricted Hartree–Fock approximation have been applied to calculate the density of states of various Co perovskite, CeCoO₃, SrCoO₃ and Sr_1-xCe_xCoO₃. We have studied the magnetically ordered states of these Co perovskites in an enlarged double cell, and find its various magnetic structures due to the occupancy of 3d band and its interaction with neighboring Co ions. In this study, we have studied the p–d hybridization of the three Co perovskites, we find t_2g electrons are localized and the flat e_g band is responsible for the itinerant behavior, and although the rare earth elements itself contribute little to the DOS at the Fermi energy, the DOS at Fermi energy and the magnetic moment changed consequently because of different valence of Co ions in these compounds and p–d hybridization effect is very important...