Theoretical Study On Transport Properties Of Iron-based Single-molecule Magnets

Due to the stable structure,discrete levels,magnetism,and other various electri-cal properties of single molecules,molecular electronics and molecular spintronics,re-garded as the next step in designing the electronic devices,become blossoming research fields aiming at exploring how electron and spin transport through single molecules.Based on different magnetic molecules,various functional molecular devices,such as molecular switch,spin filter,negative differential resistance,have been success-fully fabricated or demonstrated.Recently,single-molecule spin-crossover(SCO)com-plexes have been considered to be the promising candidates to design molecular spin-tronic devices due to their magnetic bistability between the high-spin(HS)and low-spin(LS)states.This dissertation includes the following five chapters.Here,we focus on the spin-crossover and transport properties of two Fe-based SCO complexes by per-forming extensively density functional theory(DFT)calculations combined with the non-equilibrium Green's Function(NEGF)technique.In Chapter 1,we give an overview of molecular electronics and molecular spin-tronics through introducing experimental techniques and theoretical methods,as well as various functional molecular devices.In Chapter 2,the basic conceptions of DFT and various exchange and correlation functionals are briefly introduced,and then we review the computational scheme of DFT+NEGF method for transport calculation.Finally,we introduce several DFT-based computational packages for exploring electronic structure and transport property.In Chapter 3,we investigate the spin-crossover and coherent transport properties of a six-coordinate Fe(?)complex with a N402 donor set by performing the extensive DFT calculations in combination with NEGF method.Theoretical results clearly reveal that the transition between the HS and LS states can be achieved by external stimuli in experiments.The current through the six-coordinate Fe(?)complex with the LS state sandwiched between gold electrodes is significantly less than that of the HS state due to their significantly different electronic structures.Moreover,the molecular junction with the HS state displays a robust spin-filtering effect,and the current under the small bias voltage is dominated by the spin-down electrons.Interestingly,we find that the transport properties of this examined Fe(?)complex with the HS and LS states are not sensitive to the detailed anchoring configuration,which is highly desirable in molecular spintronics.These theoretical findings suggest this Fe(?)SCO complex holds great potential in molecular spintronic devices.In Chapter 4,we explore the spin-polarized transport properties of a FeN6 molec-ular junction with the HS and LS states.Theoretical results imply that this molecular junction exhibits the molecular switching behavior,and the current through molecular junction with the HS state is significantly larger than that of the LS state.More interest-ingly,the molecular junction with the HS state exhibits a nearly perfect spin-filtering effect,and the current of the spin-down electrons is larger than that of the spin-up elec-trons.At the same time,negative differential resistance(NDR)effect is observed,which originates from the bias-dependent transmission.At the end of this chapter,we also ex-amine the interface effect on transport property,we find that the predicted spin-filtering feature remains for adding an Au atom on two electrodes surface in the molecular junc-tion.In Chapter 5,we give a short summary of this dissertation and a brief perspective for the future work in molecular spintronics.