'La_0.67Ca_0.33MnO₃/Alq₃/Co' Sandwich-Structure Organic Spin-Valves

The electron is a quantum mechanical object and has two fundamental properties, its charge and its spin. As one of the greatest achievements of humankind in the 20th century, microelectronics based on electronic charges and their transportation has greatly promoted the advancement of society and brought people into information age. But in conventional microelectronics, we only take advantage of the charge property of the electron and the spin degree of freedom of the electron is neglected. Until in 1980s the discovery of Giant magnetoresistance (GMR) had revolutionized applications in magnetic recording and memory, great interest in spin-dependent electrical transport was inspired because of its huge application potential. And this launched the new field of spin electronics-'spintronics', which is centered on the electrons' spin including their generation, transport and detection.Spintronics is based on the magnetics and microelectronics. In spintronic devices, the charge and spin of electrons can be used together to carry information. People may be able to incorporate massive storage with information processing at the same time. The advantages of the spintronic devices would be nonvolatility, increased data processing speed, decreased electronic power consumption and increased integration densities. The intrinsic binary nature of electronic spin suggests it could be used in quantum computation and communication.In order to adapt spitronics to conventional microelectronics, people make researches on spin in semiconductors. The conventional semiconductors used for devices and integrated circuits do not contain magnetic ions and are nonmagnetic. Moreover, the crystal structures of magnetic materials are usually different from that of the semiconductors used in electronics, which makes them incompatible with each other. Compared with conventional inorganic semiconductors, organic semiconductors have weak spin-orbit interaction, weak hyperfine interaction, long spin diffusion length and 'soft' matter property and they are potential candidates for spintronic applications. Researches on spin polarized injection and transport in organic spin-valves will not only have a significant impact on the applications of spintronics but also broaden our understanding on the physical hypostasis of the organic materials and bionomics.In this dissertation, we have fabricated "La_0.67Ca_0.33MnO₃/Alq₃/Co" sandwich -structure organic spin-valves using vacuum thermal evaporation method, choosing La_0.67Ca_0.33MnO₃ for the bottom electrode, cobalt as the top electrode and small Ï€-conjugated molecule 8-hydroxy-quinoline aluminium (Alq₃) as organic semiconductor spacer. An inverse giant magnetoresistance effect as large as 50% was observed at low temperature (30K) and we explicated it with Mott model. The large GMR of our device was attributed to the high spin polarization and low conductivity of the LCMO. Magnetoresistances AR/R at different temperatures were investigated and it was found that AR/R decreased rapidly with temperature increasing. The magnetoresistance expression as a function of temperature in organic spin valves was expanded and we got several demands for magnetoresistance at high temperatures. We explain why we do not find large high-field magnetoresistance and the differences of coercive field of Co electrode and thickness of organic 'ill-defined' layer.