Theoretical Study Of Transport Properties Of Magnetic Molecules

Now,the lasting miniaturization of electronic devices and the fast development of information techniques force people to discover the novel techniques and promis-ing candidates for the new-generation of electronic devices following the bottom-up approach.Due to the stable structure,discrete levels and various electrical properties,molecular electronics and molecular spintronics?the natural combination of spintron-ics and molecular electronics?become blossoming research fields aiming at exploring how electron and spin transport through single molecules.During the past years,many significant progresses have been achieved in molecular electronics,which holds great promise for the next-generation of functional electronic devices with improved perfor-mance and enhanced functionality,especially in quantum computing and high-density information storage.Various molecules have been successfully used to design vari-ous molecular devices,including molecular wires,switches,rectifiers,and transistors.Fortunately,due to the progress in enhancement of computational ability and method-s,theoretical simulations become more useful and helpful to understand and explain the transport experimental measurements as well as to design functional molecular devices.In this dissertation includes the following four chapters,and we focus on the spin-polarized transport properties of several magnetic molecules by performing exten-sively density functional theory?DFT?calculations combined with the non-equilibrium Green's Function?NEGF?technique.In Chapter 1,theoretical conceptions of DFT and various exchange and correlation functionals are briefly introduced,and then we review several DFT-based computation-al packages adopted in this dissertation.In Chapter 2,we first give an overview of molecular electronics through introduc-ing experimental methods?i.e.MCBJ and STM?and various functional devices.Then we introduce the scattering matrix approach and the?DFT + NEGF?theoretical method to explore of the transport properties through molecular junctions.In Chapter 3,we explore the electronic structures and spin transport properties of the three-shell icosahedral matryoshka cluster Pb@Mn₁₂@Pb₂₀.Previous investiga-tions mainly focused on the physicochemical properties of metal clusters.More atten-tion should be paid for their transport properties.Motivated by the magnetic clusters(i.e.C₂₈ molecule),which could act as promising candidates to build spin devices,here,we examine the three-shell icosahedral matryoshka cluster Pb@Mn₁₂?Pb₂₀.Theoret-ical results clearly reveal that Pb@Mn₁₂@Pb₂₀ has a huge magnetic moment of 28.0?B,mainly contributed by Mn atoms.The calculated spin-resolved transmission spec-tra of the Pb@Mn₁₂@Pb₂₀ junctions exhibit robust spin filtering effect,which is not sensitive to the anchoring distance and the adopted electrode materials,and the con-ductance through the cluster under the small bias voltage is mainly determined by the spin-up electrons.These findings indicate that this kind of three-shell matryoshka clus-ter with huge magnetic moment holds potential applications in molecular spintronic devices.In Chapter 4,we investigate the diarylethene-based spin crossover?SCO?mag-net Fe complex.Theoretical results clearly reveal that the conductance through the diarylethene-based SCO Fe complex with the low-spin state is significantly less than that of the high-spin state,totally differing from these contrasty to the previous inves-tigated photochromic diarylethene derivatives.The obvious spin-filtering effect and negative differential resistance behavior can be integrated in the proposed diarylethene-based SCO magnet Fe junction with the high-spin state,and in which the current is mainly contributed by the spin-down electrons under small bias voltage.Moreover,we verify the ligand-driven light-induced light-change effect in this diarylethene-based SCO magnet Fe complex,which is consistent with the experimental results.