Electronic Structure And Spin-Dependent Transport Properties Of Organic Molecular/Ferromagnetic Half-Metallic Spinterfaces

Owing to the long spin lifetime,the organic materials have potential applications in spintronic devices,which have been widely investigated.Organic spintronics is an emerging research field,which aims at combing the advantages of molecular electronics with the inherent characteristics of spintronics,which is expected to build the multifunctional spintronic devices.The interface between organic molecule and ferromagnetic metal plays an important role in the performance of spintronic devices.Therefore,it is important to fully understand the interfacial interactions and the influence of interface configurations on device performance.Fe₃O₄ and Co₂MnSi are typical half-metallic ferromagnets with Curie temperature of higher than room temperature,which has a great significance for the practical applications in spintronic devices.In this dissertation,the electronic structure and spin-dependent transport properties of the organic/ferromagnetic half-metallic spinterfaces are investigated by density functional theory and non-equilibrium Green’s function.When the C₆H₆ is adsorbed at different sites on Fe₃O₄ surface,a weak interaction between molecule and surface appears,where the half-metallic properties of Fe₃O₄are preserved.The C p_z orbitals of C₆H₆ show a spin splitting due to the hybridization of the p orbitals of C₆H₆ with the d states of Fe₃O₄.Furthermore,at the bridge site,the C₆H₆ adsorption induces a geometrical distortion of Fe₃O₄ surface,which leads to a valence transition of octahedral Fe atom in the surface layer.The electric field has a great effect on the magnetic properties of C₆H₆/Fe₃O₄interface.Depending on the electric field and the atomic position with respect to C₆H₆,the Fe magnetic moments in the surface layer decrease by different degrees.The density of states projected into the interfacial atoms shows that the electric field influences the hybridizations between Fe and O atoms in the surface layer by changing the interfacial interactions,which affects the orbital occupancy in unpaired octahedral Fe-3d electrons near Fermi level.Therefore,the Fe magnetic moments are decreased.By adsorbing a C₆H₆ on Co₂MnSi surface,the strong p-d orbitals hybridization occurs at the interface,which leads to the inversion of spin polarization at C₆H₆ site.By analyzing the d-orbital-resolved magnetic anisotropy,it is found that the great modification on the magnetic anisotropy in outmost Co₂MnSi layer after C₆H₆adsorption is mainly attributed to a change of the anisotropy contribution from d_z²orbitals.In the Fe₃O₄/4’4-bipyridine/Fe₃O₄ organic magnetic tunnel junctions,the contact configurations at the interface greatly affect the coupling mechanisms between molecule and electrode.As a result,the tunnel magnetoresistance of junctions changes both in magnitude and sign under equilibrium condition.What’s more,a large tunnel magnetoresistance of 22000%is predicted by applying electrical bias,and the junctions show outstanding spin injection efficiency.