Effect Of Electric Field On Spin Polarized Current In Ferromagnetic/Organic Semiconductor Systems

The electron is a quantum mechanical object which, apart from charge, also has a spin. Devices and integrated circuits based on the electronic charges and their transportation have been widely used in the world. Electrons and holes enrichment the transport characters of semiconductor materials. However, the electron is treated as the carrier of the charge and the spin of the electron usually are neg lected. 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 the electron spin including their generation, transport and detection. Electron spin injection and spin dependent transport are essential aspects of spintronics and have been extensively studied in a number of different contexts including: from ferromagnetic metals to superconductors; from ferromagnetic metals to normal metals; from ferromagnetic metals to nonmagnetic semiconductors and from magnetic semiconductors to nonmagnetic semiconductors or the mixture of them.Spintronics is based on the magnetics and microelectronics. In the spintronic devices, it is not the electron charge but the electron spin that carries information, and this offers a opportunities for a new generation devices using the charge and the spin of electrons together. This device may further enhance the information technology and thus create a new complexation, for example, to incorporate massive storage with information processing, or to inject spin polarized current to control the spin state of carriers. The advantages of the spintronic devices would be nonvolatility, increased data processing speed, decreased electronic power consumption, and increased inte gration densities. The intrinsic binary nature of electronic spin sugg ests it could be used as the basic unit, the qubit, for quantum computation and communication. Conventional spin valves have been widely used in computers since the mid 1990s.Compared with conventional semiconductors, organic semiconduc tors have abundant electronic, magnetic and optics characteristic andare much more easily synthesized at low temperature with little to xic waste. Based on the electronic and optical properties of organicsemiconductors, light-emitting diodes for flat-screen TVs, cell phone displays, billboards and computer display screens have been fabric ated. As the spin-orbit interaction is weak, organic semiconductors are potential candidates for spintronic applications. Spin polarized injection and transport in organic semiconductor is the next interestingtopic in spintronics. In 2002, Dediu et al. observed spin injection into thin films of conjugated organic material sexithienyl (T6) in the sandwich structure of La_0.7Sr_0.3MnO₃/T6/La_0.7Sr_0.3MnO₃ at room temperature. In 2004, Xiong et al. built a spin valve using the Alq3 as a spacer, where the Alq3 is sandwiched between layers of cobaltand half-metallic manganite La_0.7Sr_0.3MnO₃. Spin polarized injectionand transport in organic semiconductor not only can broaden our understanding on the physical world of the organic materials but alsocan have a substantial impact on the applications of spintronics and bionomics.Quantum theory used by Xie and spin diffusion theory used byRuden, Smith, and Z. G. Yu have been demonstrated successfully for studying the spin polarized injection and transport in organic semiconductors. Micro quantum theory can be used to understanding the microstructure of ferromagnetic/organic system and the dynamic of spin transport, the classic diffusion theory can be used to give the spin polarized current in the organic semiconductor structure by integrating Ohm's law.In this paper, based on the "three current model", by takes into account the special electron-spin relation in organic semiconductor and the effect of electric field, the characters of the current spin polarization are found from the classical diffusion theory(磁阻工作还没有作). The detailed research and main results are given below:1. The dependence of spin polarization on electric field with difference r in a FM/organic system.. It is found that the spin polarization increase remarkably with electric field when r is fixed. When r increase, the spin polarization increase too.2. The dependent of spin polarization on the bulk conductivities. Under the effect of electric field, the spin polarization increase dramatically when the conductivity of semiconductor increase. So choice material with largerconductivity will help the spin polarization injection.3. The dependent of spin polarization on equivalent interfacial conduct ance with difference electric field. When the interfacial conductivity increase, The spin polarization increase remarkable. And when the interfacial condu ctivity is fixed , electric field can increase spin polarization too.4. The distribution of spin polarization in the organic. We find that the spin polarization decreased from the interface into the bulk of the organic semiconductor. The spin diffusion length increase remarkably when there exits an electric field. That is to say, spin can maintain its direction for along distance. This can help to produce some appliance.