The Research Of Electronic Structure And Magnetism At LaMnO₃ Oxides Heterointerface

In recent years, with the development of the advanced technology of epitaxial film growth, on the experimental study, we can be prepared film structure on the atomic scale make use of molecular beam epitaxy and pulsed laser deposition technique, transition metal oxide interface has been widely studied. As is well-known, perovskite transition metal oxides has many interesting physical properties, such as high temperature superconductivity, ferroelectric and ferromagnetism, charge, orbital and spin ordering, giant magnetoresistance effect in La_1-xSr_xMnO₃. When two different kinds of perovskite oxide materials composed of heterogeneous interface, the interface structure of symmetry is broken, the link between the electronic effect increased, oxygen octahedral structure distortion and the phenomenon such as charge transfer, spin polarization and orbital reconstruction can happen in the system, thus in the interface appears novel quantum state different from block material. Oxide interface has potential application prospect makes it become the focus in the modern electronic information materials. In the heterojunction based on LaMnO₃, the number of Mn ions 3d electrons is 3-4, electrons occupied multiple orbitals, interface magnetic configuration is complicated. Perovskite oxide growth along ?001? or ?111? direction can produce different types of polar atomic layer, for the satisfy the stoichiometric ratio of heterointerface will happen polar discontinuous, charge transfer can be expected to gain highly spin polarization of the two-dimensional electron gas in manganese oxide heterointerface.The electronic structure and magnetic properties of several perovskite oxide interface were studied using first principles calculation based on density functional theory in this paper, the main results were as follows:?1? We studied the ion relaxation, electronic structure and magnetic properties of the ?LaMnO₃?_n/?SrTiO₃?m heterointerface. Research shows that different component thickness ratio and different interface types, lead to different degrees of ionic relaxation and electronic properties of interface is affected by this. For n type interface, when the thickness of the LaMnO₃ reaches 6 unit cell layer, the electron will transferred from LaMnO₃ to SrTiO₃, the transferred electrons occupied inter face-layer Ti-3d electronic orbital and two-dimensional electron gas appeared at interface. For ?LaMnO₃?_n/?SrTiO₃?₂ interface, with the increase of thickness at LaMnO₃, structure distortion caused by ion relaxation is reduced, and the interface between Ti atoms surrounding the electron density of states and spin polarization increases, this shows that high thickness ratio of n-type interface is helpful to produce the high mobility of two-dimensional electron gas and spin polarization. For the p-type interface ?LaMnO₃?₂/?SrTiO₃?8, there is no structure distortion in SrTiO₃ side basically and without electron transfer and spin polarization phenomenon at interface. It is found that the two types of interfaces possess 2 eV potential difference by comparing the average electrostatic potential, thus charge transfer is more difficult to occur in the p-type interface than in the n-type interface.?2? We studied the electronic properties and magnetic structure of the ?001? and ?111? direction ?LaMnO₃?m/?LaNiO₃?_n interface. The calculation results show that, ?001? direction ?LaO?+?NiO₂?^- interface and the orientation of ?111? ?LaO₃?3-/?Ni?³⁺ interface, the interface-layer of magnetic ordering turn into ferromagnetic coupling, instead of antiferro magnetic at LaMnO₃ and paramagnetism at LaNiO₃. For ?111? the direction of the interface and ?001? the direction of the interface all have electrons from LaMnO₃ side to LaNiO₃ side, suggesting that polar discontinuity also exist in the ?111? direction heterojunction, and the number of transferred charge in the ?111? direction is more, at the same time it appears highly spin polarization and ferromagnetic metallicity. The induced Ni magnetic moment value for ?111? the direction of the interface is bigger than ?001? the direction of the interface, and the magnetic moment size controlled by the thickness ratio m/n, calculation shows that the ?111? direction interface for ?2:1? structure can achieve maximum Ni magnetic moment.