First Principles Calculations On Electronic Structure Of3d Transition Metal Oxides

Due to the development of the information storage density, a great deal of interestis focused in spintronics devices which combine the basic characters of charge and spin.A high efficient spin injection is urgently required in spintronics. However, low Curietemperature, unclear origination of ferromagnetism and interface conductivity mismatchmake the diluted magnetic semiconductors and half–metal materials deficient inpractical applications. One of the hot topics is to obtain high spin polarization and tounderstand the change of spin polarization at interface of the heterostructures.In this dissertation, the electronic structure of doped antiferromagnetic oxidesincluding CuO, NiO and α–Fe2O3was calculated by first principles calculations toprovide the theoretical basis. The interfacial coupling effects on the magnetic andelectronic structures of Fe3O4/BiFeO3(001) superlattices and Fe3O4/grapheneheterostructures were studied, which can provide the theoretical basis for theexperimental design.By calculating the band structure, density of states and optical properties oftransition metals doped antiferromagnetic oxides NiO and α–Fe2O3, it was found thatthe incorporation of Cu into NiO can produce spin polarization, resulting in thehalf metallic character in Cu doped NiO, which originates from the orbit hybridizationbetween Cu–3d and O–2p states. When Cu and Cd were doped into α–Fe2O3, thesystems became half metallic, which can enhance the absorption capacity in the visiblerange and improve the photoelectrochemical performance. The research on the magneticand electronic properties of Cu1xFexO shows that spin polarization exists in both singleand double Fe doped CuO. The magnetic properties and spin polarization can beattributed to the double exchange coupling between Fe2+O2Cu2+in single Fe dopedCuO, which should come from the double superexchange interactionFe2+O2Cu2+O2Fe2+in double Fe doped CuO.The calculations on the magnetic and electronic structure of Fe3O4/BiFeO3(001)superlattices show that the ferromagnetic changes are mainly from the bonding andcharge transfer among the interfacial atoms. Total magnetic moment inFe3O4/BiFeO3(001) superlattices is increased and the largest enhancement is13%, which is affected by interfacial oxygen content that can affect the bonding amonginterfacial atoms and charge transfer, making the magnetic moment of Fe3O4increase.Therefore, interfacial oxygen content plays an important role in determining theinterfacial coupling. In Fe3O4(111)/graphene heterostructure, magnetic moments changewith interface terminals. The magnetic moments of all the three Fe3O4(111)/graphenesystems are enhanced and the largest enhancement is18.5%. Herewith, the Fe(A)magnetic moment has a major change, which can be attributed to the less O atoms thatsurrounds Fe(A) atoms than Fe(B) atoms. Furthermore, the spin polarization of Fe3O4atthe interface is lowered, indicating that interface terminations play an important role indetermining the magnetism and spin polarization of the heterostructures.