Electronic Structure And Magnetic Properties Of Perovskite Materials/Fe₃O₄ Heterointerfaces

Perovskite materials become one of the most widely used electronic ceramic materials due to its high dielectricity,piezoelectricity and ferroelectricity.The multifunctional oxide Fe₃O₄ can form heterostructure with perovskites,which exhibits many novel and complicated physical properties at the interface.Recently,the modulation on the interfacial effect via strain or electric field is one of the hot topics,which is important to the development of spintronic field.In this dissertation,the electronic structures of Fe₃O₄/BaTiO₃ and CH₃NH₃PbI₃/Fe₃O₄（MAPbI₃/Fe₃O₄）were calculated by density functional theory.Electric field or biaxial strain modulated interfacial electronic structure and magnetic properties of heterostructures were investigated systematically.Firstly,the electronic structure of Fe₃O₄/BaTiO₃ heterointerface has been investigated.All of the models（TiO-Fe_A,OTi-Fe_A,TiO-Fe_BO and OTi-Fe_BO）are stable,where TiO-Fe_BO is the most stable one.In the TiO-Fe_BO model,BaTiO₃ has a spin polarization of 100%.The spin polarization of the interfacial Ti keeps at an electric field of-100¹000 kV/cm,which disappears at-500 and-1000 kV/cm.The tunable high spin polarization at Fe₃O₄/BaTiO₃ interfaces is related to the ferroelectricity of BaTiO₃.Secondly,the biaxial strain effect on Fe₃O₄/BaTiO₃ heterostructures has been studied,two models（OTi-Fe_BO and TiO-Fe_BO）are investigated.Tunable half metallicity（HM）and orbital rearrangement of interfacial layers appears in the strained OTi-Fe_BO model.The OTi-Fe_BO model keeps the half metallicity at-6%,-4%,-2%and 2%strain,but disappears at 4%and 6%strain,the orbital overlapping of interfacial Fe atoms appears at 2%strain.The transition from HM to insulator can be attributed to the t_2g orbital rearrangement induced by octahedral distortion due to the interfacial interaction.Finally,the electronic structure of MAPbI₃/Fe₃O₄ heterointerface is calculated.All the models（PbI₂/Fe_A,MAI/Fe_A,PbI₂/Fe_BO and MAI/Fe_BO）are stable,where PbI₂/Fe_A is the most stable one.The transition from half metallicity to semiconductor of Fe₃O₄ appears in PbI₂/Fe_A model,where the spin-up and spin-down bandgaps are1.20 and 0.75 eV,respectively.External electric field can modulate the band structure of PbI₂/Fe_A model,where a direct-indirect bandgap transition of Fe₃O₄ appears at 500kV/cm.The direct spin-up bandgap will change to indirect one,which is opposite to the spin-down bandgap.