Spin-Polarized Transport And Spin Dynamics In Magnetic Nanostructures

The spin-polarized transport properties is one of the important research issues in condensed matter physics.Until recent years,with the rapid development of information technology and nanofabrication technology,the charge-based semiconductor industry is fast approaching the physical limits of transistor miniaturization,the electron spin degree of freedom is gradually renewed awareness and development.There is strong demand to use the spin of the electron rather than charge to carry the information and to improve the performance of electronic devices,such as increasing the density of integration,speedup data processing,and reduce energy dissipation.Therefore,the spin-polarized transport properties and spin dynamics in magnetic nanostructures are of great significance.In this thesis,spin polarized transport and spin dynamics magnetic nanostructures are investigated as follows.Firstly,we theoretically investigate spin-dependent transport in quasiperiodic cascade junctions of a ferromagnetic metal(FM)and semiconductor(SC),where FM and SC are arranged in the Fibonacci sequence.It is shown that spin-up and spin-down electrons possess different bandgap structures against the Rashba spin-orbit wave vector.The spin-dependent bandgap structure has the hierarchical characteristic and present self-similarity.Due to the quasiperiodicity,multiple resonant transmissions for spin-up or spin-down electrons can be observed within the bandgap;thereafter,spin polarization has multiple reversals.And it is also found that the electrical conductance can come from one kind of spin electrons around the resonant wave vector.These investigations may provide a unique way to design the devices such as spin filters and spin switches.Secondly,we theoretically investigate the spin-split energy bands of electrons and spin-polarized transport in two-dimensional spin-orbit lateral superlattices(SOLSLs),where the square rods with Rashba spin-orbit coupling(SOC)are distributed periodically by applying gate voltages on the semiconductor.It is found that the energy minibands are formed and the energy levels are split up by the Rashba SOC.As a result,the spin-polarized conductance is obtained even in the absence of external magnetic fields and magnetic materials.Meanwhile,the spin polarization can approach high values in the SOLSLs by manipulating the strength of SOC.Furthermore,the spin-dependent electronic charge distributions have been obtained,which present a clear picture of spin-polarized conductance.Interestingly,by introducing a magnetic modulation,conductance curves for spinup and spindown electrons are translated in the different directions.As a result,high spin polarization is observed,and fully spin-polarized conductance is achieved in this 2DSL.Furthermore,the electronic wavefunctions have been obtained which presents a clear picture of spin filtering.Our investigations achieve potential applications in spin quantum devices and spin filters.Finally,we theoretically investigate the dynamics of magnetic vortex in a double-plate nanostructure,in which two square permalloy plates are joined together by imposing closely on a thin permalloy film.It is found that magnetic vortices have been formed in the two square permalloy plates.Due to the involving of the joint,the out-of-plane magnetization can also be observed at the sidewalls between the square plates and the joint area.The ground states with the vortex polarities(1,1)and(1,-1)are obtained when the thickness of the joint area is varied.By applying a short in-plane magnetic field pulse,the vortices deviate from their equilibrium positions and gyrate with damping radius.Interestingly,the vortex polarity can be switched if the strength of magnetic field approaches the threshold of switching field.Particularly by changing the strength of magnetic field,the two vortices can be switched alternatively in the double-plate nanostructure.The investigations may provide potential applications in magnetic vortex memories.In summary,we present spin polarized transport and spin dynamics magnetic nanostructures.We study the resonant transmission of electrons in the quasiperiodic metallic nanowires,and systematic study the impact of the structure of the nanowires on transmission.And then we investigate spin polarized transport in the quasiperiodic ferromagnetic metal/semiconductor cascade heterostructure.Theoretical analysis and numerical calculation of the spin-dependent band structure formation process,as well as spin dependent band structure of spin polarized transport properties.Meanwhile we reveal the influence of the energy band structure on spin-polarized transport properties,and gives a physical image to the generation of the spin-polarized conductance.And the dynamics of magnetic vortex in a double-plate nanostructure has been theoretically investigated.We found that due to the involving of the joint,the out-of-plane magnetization can also be observed at the sidewalls between the square plates and the joint area.By applying a short in-plane magnetic field pulse,the vortices deviate from their equilibrium positions and gyrate with damping radius.Interestingly,the vortex polarity can be switched if the strength of magnetic field reaches the threshold of switching field.Particularly by changing the strength of magnetic field,the two vortices can be switched alternatively in the double-plate nanostructure.The results of these studies may have potential applications in quantum devices.