Spin Transport Properties In Vacancies Zigzag Silicene Nanoribbons

The spin transport properties of pristine and vacancies zigzag silicene nanoribbons(ZSi NRs) in the ferromagnetic(FM) and anti-ferromagnetic(AFM) ground states are investigated using the nonequilibrium Green’s function(NEGF) method combined with the density functional theory(DFT). We consider two probe systems with FM electrodes in the parallel(FM-P) and antiparallel(FM-AP) configurations or AFM electrodes in the parallel(AFM-P) configurations. We study mainly the crystal reconstruction and the spin transport properties in the presence of monovacancies, divacancies and linear-vacancies in a zigzag silicene nanoribbon(ZSi NR) with a transversal two-fold rotation symmetry with respect to its central axis. We study also the dependence of the electron transport on the position of vacancies.In this thesis, I firstly review briefly the discovery, experimental preparation and novel electronic properties of silicene. Then we introduce the ATK software, the simulation tool we used, and the density function theory(DFT) and nonequilibrium Green’s Function(NEGF) implemented in the package. Afterward, the works done during my graduate study are presented as follows:The crystal reconstructions in the presence of vacancies in a zigzag silicene nanoribbon(ZSi NR) with transversal symmetry have been simulated and their influence on the electric transport and thermoelectric properties have been assessed by the nonequilibrium Green’s function method combined with the density functional theory. The spin dependent conductance, magnetoresistance, current-voltage curves and the Seebeck coefficient have been calculated. Our results show that a 5-atom-ring is formed in monovacancies, a 5-8-5 ring structure in divacancies, and a 8-4-8-4 ring structure in linear-vacancies. The linear conductance becomes strongly spin dependent when the transversal symmetry of the ribbon is broken by the vacancies especially if they are located on the edges. The colossal magnetoresistance between the FM and AFM states remains in all the cases but the giant magnetoresistance between the FM-P and FM-AP can be smeared by asymmetric vacancies. A single-spin negative differential resistance is predicted in systems with AFM electrodes of asymmetric ZSi NRs in the presence of vacancies. A strong spin Seebeck effect is expected at high temperature in ZSi NRs with linear-vacancies.Meanwhile, we have studied the dependence of the electron transport on the position of vacancy. In the FM-P configuration, the systems are translationally symmetric and the linear conductance is independent of the vacancy position. In contrast, in the FM-AP configuration, the conductance becomes very sensitive to the vacancy position especially for vacancies near the transition point of magnetization. In the FM-AP configuration, a strong spin Seebeck effect can be expected.