Transport In The Tunneling Junction With Two Single Molecular Magnets

Single molecular magnet(SMM) is a kind of single-molecule material with strong in-trinsic magnetism. This kind of molecular material has been found for about twenty years. It attracts many physicists for its special bistable state energy structure and inter-esting transport properties, which are different from traditional quantum dots. Compar-ing to the conventional organic molecular materials, the single molecular magnet (S-MM) has been shown to be a suitable component for future molecule-based spintronic devices. Due to its spin selective properties, the SMM seems to be a very appropriate candidate for designing spin filters or spin valves.In chapter1we give an introduction to investigational background and some ba-sic conceptions. The single molecular magnets have the structure of bistable energy states. At low temperature, the SMM is trapped in one of the potential wells for spon-taneous symmetry breaking, presenting a large intrinsic magnetic momentum which results in a high spin reversal barrier. A lot of theoretical and experimental research-es have been done based on this kind of molecule device and a lot of phenomena are predicted or detected, such as Single electron transistor(SET),spin Seebeck effec-t, high Kondo temperature, pure spin current generator, magnetization reversal driven by spin-polarized current. With the development of nano technology such as the spin-polarized scanning tunneling microscope(SP-STM) and the inelastic electron tunneling spectroscopy(IETS), the spin orientation of a single magnetic atom or a single molec-ular magnet can be controlled via the spin-transfer torque (STT) effect. According to its controllable properties, it can be good candidate for the spintronic and information processing device. In chapter2we give an introduction for the related theoretical methods:master equation approach.In chapter3, we studied the transport through two same single molecular mag-nets, connected to two normal metal leads in series arrangement. Applying low bias voltage, the junction presents low/high resistant state with the SMMs’initial states parallel/antiparallel. This phenomenon is similar with the transport in ferromagnetic parallel/antiparallel junctions. Strong Coulomb repulse suppresses the current in an-tiparallel situation to nearly vanish. At high bias voltage, the middle system containing two SMMs tends to be non-polarized, and acts like ordinary quantum dots. The junc-tion supplies a probability for the memory device.In chapter4, we theoretically explore the spin transport in nano-structures consist-ing of two single-molecular magnets(SMM) sandwiched between a couple of nonmag-netic electrodes. The reversal of the SMM’s spin arises from the spin-transfer torque effect, and it is realized via a set of transitions between the SMM’s spin states, which must satisfy the basic selection rules,△m=1/2and△n=1. In low bias regime, the magnetism of SMM with smaller spin flipping barrier exhibits a hysteresis loop with bistable magnetic states. And the sign reversal of magnetization corresponds to a certain electron current arisen through the junction. By adjusting bias voltage,the magnetic structure of two SMM can be set in parallel/anti-parallel configurations,and the tunneling currents can also be turns on/off by the different magnetic structures. It is shown that the spin states of the SMM in the tunnel junction can be manipulated by the bias voltage, to be parallel or antiparallel to the magnetization of each other. Such a manipulation is driven by a spin-related electron transport between electrons and mag-netic molecules, and needs neither external magnetic field nor magnetic electrodes in the structure.The same physics may also be responsible for the spin-valve phenomena discovered recently in two rare-earth SMMs. And the SMMs with bistable magnet-ic states controlled by bias voltage are expected to be information units in the future spintronic device.The last chapter presents a summary of this dissertation, and then gives some outlook for the investigation.