Study On Tunneling Magnetoresistance And Tunneling Time In Magnetic Tunnel Junctions Containing Ferromagnetic Semiconductors

Based on the transfer matrix method and the coherent quantum transfer theory,the tunneling magnetoresistance resistance(TMR)and the tunneling time(phase time and dwell time)in ferromagnetic metal/insulator/ferromagnetic semiconductor/ordinary metal(FM/I/FS/NM)magnetic tunnel junctions are studied.The effects of thicknesses and the molecular fields of the ferromagnetic semiconductor layer,the thicknesses and the barrier heights of the insulating layer,and the Rashba spin-orbit coupling on the TMR and tunneling time are calculated.The main contents of this paper are as follows:In the first chapter,we briefly introduce the generation and development of spintronics,and then explain what is the Rashba spin-orbit coupling effect and what is the spin-filtering effect,and then briefly describe the Julliere model and Slonczewski nearly free electron approximation model.Finally,the research backgrounds of tunneling time are introduced.In the second chapter,on the basis of existing researches of ferromagnetic metal/insulator/ferromagnetic insulator/normal metal(FM/I/FI/NM)single spin-filter magnetic tunneling junctions,the FI layer in FM/I/FI/NM single spin-filter magnetic tunneling junction is replaced with FS layer and the effects of tunneling magnetic resistantces(TMRs)in ferromagnetic metal/insulator/ferromagnetic semiconductor/normal metal(FM/I/FS/NM)magnetic tunneling junction are studied.The results show that,as the influences of the spin filter and the Rashba spin orbit coupling effects in the FS layer,a large TMR can be obtained for large FS layer thickness and the manufacturing difficulties brought by the too small thickness of FI layers in the usual FM/I/FI/NM(FI represents the ferromagnetic insulator layer)single spin filter junction can be avoided.The results also show that,for the FM/I/FS/NM junctions,the TMR would oscillate with the FS layer thickness,the Rashba spin orbitcoupling strength,the molecular field and would tend to saturation with the increasing of I layer thickness.In the third chapter,based on the free electron approximation and Winful's tunneling time model,spin-dependent tunneling time in the ferromagnetic metal/insulator/ferromagnetic semiconductor/common metal(FM/I/FS/NM)tunnel junction are studied further.The results show that,The tunneling time oscillates with the change of the incident energy of the electron;the variation of the tunneling time with the height of the barrier of the insulating layer,the influence of the self-coherent term on the upper spin electron is greater than that of the lower spin electron;as the thickness of the insulating layer changes,due to the Hatman effect,the tunneling time appears saturated;the molecular field size in the ferromagnetic semiconductor FS layer and the Rashba spin-orbit coupling intensity have little effect on the tunneling time.