Effect Of Spin-orbit Coupling Interaction On The Transport Properties In The Multilayer Magnetic Tunnel Junctions

With the development of science and technology, the size of microelectronic device is gradually reduced. The new phenomena for the electronic transport in mesoscopic area and the spin-polarized transport characteristics have been paid much attention in recent years. In order to better control the electronic spin in those new type semiconductor electronic devices, we need to deeply understand the spin-dependent transport properties.In this thesis based on the quantum coherent transport theory and the transfer-matrix method, the properties of electronic transport in the magnetic tunnel junction are theoretically investigated. The main contents in this paper are as follows:In the first chapter, we first briefly introduce the development of spintronics. Then the Rashba spin-orbit coupling effect and the spin-filter effect are discussed. Following, the two kinds of theoretical model, i.e. Julliere model and Slonczewski free electron model about the tunneling magnetoresistance are presented respectively.In the second chapter, we use the Slonczewski free electron model and the transfer-matrix method to study the tunnel magnetoresistance (TMR) and the transmission conductance through the normal metal/ ferromagnetic semiconductor )/ insulator/ ferromagnetic semiconductor/ normal metal double spin-filter tunnel junction. The results of the numerical calculation show that: as the Rashba spin-orbit coupling effect and the spin-filter effect in the ferromagnetic semiconductor layers, the double spin-filter tunnel junction has the large TMR. When the thicknesses in the both ferromagnetic semiconductor layers are equal, we can get its maximum value of the TMR. The tunneling magnetoresistance and the tunneling conductance can appear oscillation phenomena with the Rashba spin-orbit coupling strength changing. As the Rashba spin-orbit coupling strength increases, the TMR and the tunneling conductance oscillate fast and the periods of oscillations become more and more short. As the same time, the oscillation amplitude of tunneling conductance changes a little, but the TMR obviously changes.In the third chapter, using the same method as that in the second chapter, we investigate the relations of tunneling effects with the thicknesses of the semiconductors and the spin-orbit coupling strength in the ferromagnetic metal / semiconductor / insulator / semiconductor / ferromagnetic metal tunnel junction. The results of the numerical calculation indicate that: with the variation of the thickness and the spin-orbit coupling strength of semiconductor layers, the tunneling magnetoresistance and the tunneling coefficient appear oscillation phenomena. When the spin-orbit coupling strengths in the both semiconductor layers are equal, the numerical values of TMR are always positive. But when the spin-orbit coupling strengths in the both semiconductor layers are not equal, the large negative TMR effect can appear. In addition, when the ratio of Rashba spin-orbit coupling strengths between the two semiconductors increases, the oscillation amplitudes of variation of TMR which are related to the thicknesses of the semiconductor layers are significantly enhanced.