Theoretic Research On Spin-polarized Transport Properties Of Organic Magnetic Molecule Device

The electron is a quantum mechanical object which, apart from charge, also has a spin. Devices and integrated circuits based on electronic charges and their transportation have been widely used in the world. Electrons and holes enrichment the transport characters of semiconductor materials. However, electron is treated as carrier of charge and spin of electron usually are neglected. The discovery of GMR (giant magnetoresistance) and TMR (tunneling magnetoresistance) in metallic spin valves have revolutionized applications such as magnetic recording and memory, and launched the new field of spin electronics—'spintronics', which is centered on electron spin including their generation, transport and detection.Organic Spintronics is focused on researching of spin of organic molecules with basis of spintronics research. Comparing to inorganic materials, organic molecules have some distinguished advantages, such as small-density, light-weight, and hard to be oxygenated and so on. And they have abundant properties in electronics, optics and magnetics, with good applications in OLED and display device and so on. In addition, because of their weak spin-orbital coupling, organic semiconductors have become one of best candidates for spin polarized transport materials. Thus, exploring organic semiconductors to be molecule device is one of most promising researches in spintronics. It has a significant effect on understanding the physics of organic materials, mastering the functions and applications in spintronics and life science to study transport properties in organic magnetic molecule materials.In this thesis, we developed the research on the device made of one classic organic molecule, poly-BIPO, from the basis research of the material done by our laboratory, we considered the strong electron-phonon coupling of the organic material, the spin correlation between electrons and the residual spins of side radical R's, also the electron-electron interaction in the main zigzag chain. The system attached to two one dimensional semi-infinite metal electrodes. We used the extended Su-Schrieffer-Heeger (SSH) model to describe the molecule chain, and combine the Green's function formalism, with the Landauer-Buttiker formula to calculate the current-voltage (I-V) curve of the M/OF/M device. After that, we investigated the factors influenced transport properties of the device, to understand the magnetic properties of the organic material better. First we studied the spin polarization of current through the device, to see if it has potentials to be constructed to a spin dependent device. Then we explored some basic factors influenced transport properties of the device. And we found that spin coupling between main chain and side radical J_f , electron-phonon coupling a, interfacial coupling t_l/r and spin direction can always influence transport properties of the device. At last, we paid special attention to spin flipping of side radicals, which can have a distinguished effect on the transport properties of the device, because spins of side radicals are the key factor to make the material ferromagnetic. We noticed that spin flipping would truly influence the I-V curve of the device. With different arrangement of spin flipping, the current even became 100% negative polarized from 100% positive polarized. It is a exciting result because we can control the current polarization by switching the spin direction of side radicals. It has a valuable worth on the application of molecule spintronics.