Abstract
Spin current and spin transfer torque play important roles in spintronics application. The spin current carries angular momentum, which can be transferred to the magnetization it passes through, a phenomenon known as spin-transfer torques. Generally, spin current can be generated by simply passing a charge current through a ferromagnetic metal (FM). A more efficient way to generate spin current is to utilize spin Hall effect (SHE) observed in the materials with strong spin orbital coupling (SOC) such as heavy metals (HM), which produce pure spin current transverse to the applied charge current. Recently, the novel material topological insulators (TIs) have been regarded as the even more promising candidates for generating pure spin current with extremely high spin charge conversion efficiency due to its surface state property. The spin transfer torque can be not only used in magnetization switching, but also driving persistent oscillations of magnetization. In this dissertation, the spin transfer-torque-induced ferromagnetic dynamics were investigated via the spin-transfer-torque ferromagnetic resonance (ST-FMR) technique on several bilayer thin film systems, including HM/FM, TI/FM in which the both layers are conducting and the important material property for the non-ferromagnetic layer, efficiency of charge-torque conversion can be well-evaluated. In these systems, the analysis of ST-FMR spectrum stems from the anisotropic magnetoresistance (AMR)-mediated spin diode effect in the FM layer. On the other hand, a novel bilayer system comprised of HM/ferromagnetic insulator (FI) was also investigated using the ST-FMR. Unlike the conducting bilayers, this system only allows current pass through HM layer. The newly proposed theoretical model based on spin-Hall magnetoresistance (SMR) was examined and then modified in our analysis. The finding provides a more accurate approach for using SMR model on ST-FMR measurement. The study provides a basis for the ST-FMR experiment on the novel bilayer structure combined with TI and FI.