UC Irvine

Spin current is the flow of electron spin angular momentum. It can either be partially spin polarized current generated due to the exchange interactions of spins and local magnetization, or pure spin current generated from spin orbit interaction. Both sources of spin current are under intensive study for their efficient interaction with nanoscale magnetic structures, and potential application of magnetoresistive random-access memory (MRAM), spin torque nano-oscillators (STNOs) and other innovative devices.

In this dissertation, spin Hall effect mediated magnetization dynamics in Platinum/Permalloy nanowires are excited by different means and studied experimentally. This includes stead state self-oscillation of magnetization in a ferromagnetic nanowire serving as the active region of a spin torque oscillator driven by spin orbit torques. Our work demonstrate that magnetization self-oscillations can be excited in a one-dimensional magnetic system and that dimensions of the active region of spin torque oscillators, for the first time, can be extended beyond the nanometer length scale. We also demonstrate that via proper design of the nanowire shape, which results in spatial non-uniform spin current density, we can significantly decrease the phase noise of spin orbit torque oscillators. It also stabilizes the single-mode generation regime, and points out a path for partial control of multi-mode excitation in nanostructures. We also parametrically excite magnetization dynamics in the nanowires, and it demonstrates that nonlinear dynamic magnetic effect can have a larger efficiency than the direct linear excitation in spin Hall structures, and it provides additional information about excited spin wave mode systems owing to its threshold nature that is unavailable from direct excitation.