Spin-Polarized Transport And TMR Effect In Mesoscopic System

Spin-dependent transport is an active field in spintronics. In this dissertation, we first introduce the development of spintronics and some typical properties of spin polarized transport in the mesoscopic system. Some concepts, such as Magnetoresistance, Rashba and Dresselhaus spin-orbit coupling and some definitions of spin tunneling time, are reviewed. Using the method of one-dimensional quantum wave guide theory, we investigate in detail the spin-polarized transport and tunneling time for the F/S/F nanostructure heterojunction and mesoscopic ring, which not only has potential application but also has important significance for the research of basis theory.(1) Considering spin-orbit interactions and interface barrier, we study spin-transport properties through F/S/F nanostructure. The numerical results indicate that the electron spin can be inversed for high interface potential barriers and a single resonant peak of electron transmission probability appears when changing the spin-orbit coupling. With the variation of angle between the magnetic directions of two ferromagnetic layers, TMR changes from positive value to negative value atθ=πand the absolute value of TMR is asymmetry aboutθ=π, which properties are induced by Rashba spin-orbit coupling but not by Dresselhaus spin-orbit coupling. In additional, the Rashba spin-orbit coupling can enhance the effect of magnetoresistance.(2) We investigate the tunneling time through F/S/F heterojunction by comparing the cases of presenting and absenting the spin-flipping effects. As a result, with increasing of semiconductor length, the spin tunneling time does not increase linearly but shows a wavy growth process when being absent of spin-flipping. When considering the effect of spin-flipping, the spin tunneling time will oscillate drastically, even in some regions the declining trend appears. The spin tunneling time for spin-up and spin-down electrons is different and can be separated.(3) It is also investigated that the polarized electron passes through the AC ring with two parallel or antiparallel ferromagnetic leads. The transmission coefficients can be controlled by the magnitude and direction of electron field. At the large tilt angle x of electric field, TMR as the function of magnitude of electric field can vary from positive to negative. When fixing the magnitude of electric field, TMR also can alternate plus and minus signs and be symmetric about x=πwith the variations of tilt angle of electric field.