Theoretical Study Of Spin Injection In T-shaped Organic Device

Microelectronics, which based on the electron charge and ignores the characteristicsof the electron spin, has achieved great success in the20th century. The discovery ofGiant magnetoresistance and the tunnel magnetoresistance lead to a revolution in the fieldof magnetic storage and magnetic recording. After that people had a great interest andenthusiasm in the properties of the electron’s spin, and a new discipline-spintronics wasestablished.Spintronics is a discipline about the control, transport and measurement of theelectron spin. In the field of microelectronics, the problem is that the electronic quantumeffects would occur if the device size was reduced into the nano-scale, and that issueaffects the future development of large scale integrated circuit. Compared with the charge,spin has many advantages, such as faster data processing, low energy consumption andhigh integration, good stability et al. Using electron spin will create new physicalsemiconductor devices even achieve quantum memory and quantum computing. Thespintronics will likely replace microelectronics in the mainstream of the industry. Toachieve these aspirations, people must achieve spin polarized electrons, so the mostwidely and popular spintronics is the spin injection and transport. Spin injectionconfigurations include spin injection from ferromagnetic metal into non-magneticsemiconductor, ferromagnetic metal into conductor, ferromagnetic metal intosuperconductor, magnetic semiconductor into non-magnetic semiconductor et al.The ferromagnetic/non-magnetic semiconductor basic configuration is generallyused in semiconductor spin injection. However, there’s conductivity mismatch problem inthis configuration and scientists solve this problem by adding a thin layer at the interface.Compared with inorganic semiconductors, organic semiconductors have many advantages,such as strong deformation ability, easy treatment of a large area, easy to produce a thin film device, high toughness, good mechanical adaptability of the device, easy to form nicetouch with the contact layer through self-regulation, et al. Organic semiconductors havelow spin-orbit interaction and weak hyperfine interaction, therefore, organicsemiconductors are ideal injection materials. In the year2002, Dediu firstly studied thespin injection and transport in organic materials T6(sexithienyl), and ferromagneticmaterial La0.7Sr0.3MnO3(LSMO) was used as electrodes. Theoretically, people usequantum theory and spin diffusion and drift theory to study the spin injection andtransport in ferromagnetic/organic systems.In recent years, people have done a lot of work on spin injection and transport, butthe spin injection efficiency is low at room temperature. Based on the spin diffusion anddrift theory and Ohm’s law, we studied the spin injection characters in a T-shaped modeland made a comparison with the results in normal ferromagnetic/organic hetostructure.Effects of the electrical and magnetic fields on the spin injection are also discussed.Details are as follows：1. Improvement of the spin injection efficiency in a simple T-shaped organic devicemodel.A simple T-shaped model of organic spin injection device is constructed.Spin-polarized currents are injected from one branch, and ejected out from the other twobranches. The improvement of the spin injection efficiency can be obtained by adjustingthe ratio of the currents in the two ejected branches. Based on the spin diffusion and driftequations and Ohm’s law, the current spin polarization at the ferromagnetic/organicinterface in the T-shaped model was studied and also the comparison between theT-shaped model and the normal ferromagnetic/organic hetostructure was made. From thecalculation, it was found that the current spin polarization in the T-shaped model is higherthan that in normal ferromagnetic/organic hetostructure, and the spin injection efficiencycould be enhanced by adjusting the electric field, the polaron ration in the organicsemiconductors, the conductivity et al.2. Effect of magnetic fields on the spin injection efficiency in the T-shaped organicdevice. Based on the spin diffusion drift equations and Ohm’s law, effect of magnetic fieldson the spin injection efficiency in the T-shaped organic device was studied. The currentspin polarization was increased with the increasing of the magnetic fields, and otherfactors that affect the spin injection under magnetic fields were also discussed.3. Spin injection and transport in a double T-Shaped organic spintronic devicemodel.Based on the T-shaped model of organic spin injection device, we constructed adouble T-Shaped model. Effects of the branch current ratio and the polaron ratio on thespin injection efficiency were studied from spin diffusion equations and Ohm’s law.