Theoretical study of spin dependent transport in nanoscale spintronic systems

Abstract

Spintronic devices make use of the spin properties of electrons besides its charge properties. They are novel devices which potentially have faster operation speeds, low energy consumption and smaller size.

In this thesis, we focus on the spin dependent transport (SDT) through magnetoresistive (MR) devices, quantum dot based tunnel junction (QD-TJ) systems and ferromagnetic single electron transistors (FM-SETs). For these spintronic devices, the SDT models are theoretically established based on the Boltzmann equation method, the Keldysh nonequilibrium Green's function (NEGF) formulism and the master equation (ME) approach. These SDT models systematically integrate the electron transport, the electron-electron interactions, the devices properties (such as the spin polarization of materials, the coupling asymmetry of the junctions and the noncollinearity of the magnetization alignment), and the spin depolarization effects. Detailed analysis and discussions were done for the SDT properties (such as the I-V characteristics and MR) and their dependence on various devices parameters. Based on those results, possible methods are proposed to enhance the MR of magnetoresistive spintronic devices, to generate fully spin polarized current by utilizing the combined effect from SDT and single electron tunneling, and to reduce the leakage current in a SET by SDT. These theoretical proposals are expected to serve as references for future theoretical and experimental studies in spin valves (SV)s, QD based TJs, and SETs.