Electron-spin Polarization Effect In Magnetic Nanostructures Modulated By Spin-orbit Couplings

Semiconductor spintronics is a new multidisciplinary field,which mainly investigates the control of electron-spins in semiconductor materials and makes a new generation of spintronics devices by using the spin properties.Comparing with existing electron devices,spintronics devices possess more advantages due to the usage of the spins,such as faster data-processing speed,larger information-storing capacity,higher integrated density and lower power consumption.However,the operation of a spintronics device requires the spin-polarized electrons in the semiconductor materials.While the spin states of electrons in the semiconductor materials are usually degenerate,therefore,how to produce and manipulate spin-polarized electrons into the semiconductor materials is an urgent question that needs to address in spintronics applications,and also gives rise to a significant research direction in the field of spintronics.This thesis chooses two typical kinds of magnetic nanostructures(magnetic-barrier nanostructure and hybrid magnetic-electrical-barrier nanostructure)as the research objects to investigate the manipulation of the intrinsic spin-orbit coupling(briefly called the SOC term,including Rashba type and Dresselhaus type)to the electron-spin polarization effect in magnetic nanostructures by adopting the theoretical analysis combining with the numerical simulation,which aims at designing and exploiting controllable spin-polarized source---spin filter for spintronics applications.It consists of five chapters.Chapter one is an introduction,which briefly introduces spintronics,the magnetic nanostructure and the progress of the electron-spin polarization effect achieved in this kind of nanostructures,and the main research contexts of the thesis.In chapter two,we mainly introduce the research methods exploited in the thesis,including two aspects: the improved transfer-matrix method(ITM)and the Landauer-Büttiker conductance theory on the microstructure(LB).By taking the δ-function magnetic-barriers as an example,chapter three researches the electron-spin polarization effect in SOC-modulated magnetic-barrier nanostructures.This magnetic nanostructure can be experimentally formed by depositing two nanosized ferromagnetic stripes with the horizontal magnetization on the top and bottom of the semiconductor InAs heterostructure,respectively.All transmission coefficient,conductance and electron-spin polarization are obtained analytically.The calculated results show that the degree of the electron-spin polarization can be manipulated by changing the strength of the Rashba and/or Dresselhaus SOCs in the magnetic-barrier nanostructure.Therefore,the magnetic-barrier nanostructures can be employed as the SOC-controllable spin filters.In chapter four,as an example of the hybrid magnetic-electric-barrier(MEB)the δ-function magnetic-barrier and the rectangular electric-barrier are taken into account,and the effect of Rashba and Dresselhaus SOCs on the behavior of the spin-polarized electrons in hybrid MEB nanostructures.In experiments,such a magnetic nanostructure can be realized by depositing a nanosized ferromagnetic stripe with a horizontal magnetization and a nanosized Schottky metal stripe under an applied D.C.voltage in a parallel configuration,on the top of a semiconductor InAs heterostructure.Rashba and Dresselhaus SOCs dependent transmission probability,conductance and degree of the electron-spin polarization are calculated by exactly solving Schr?dinger equation and with the help of the transfer-matrix method.It is shown that not only the magnitude of the electron-spin polarization but also its sign varies with the strength of the Rashba and Dresselhaus SOCs in this hybrid MEB nanostructure.Thus,the degree of electron-spin polarization can be manipulated by properly adjusting the Rashba and/or Dresselhaus SOCs.Moreover,this kind of magnetic nanostructures can also be designed as the SOC-controllable electron-spin filter.Finally,chapter five briefly summarizes the research work of the whole thesis and achieved results.On the other hand,the problems that exist in this thesis and furthering study direction in the future are also pointed out.