UC San Diego

The development of the spintronic-based data storage devices such as spin transfer torque magnetoresistive random access memory (STT-MRAM) is being driven by the surging data consumption and demand for faster data processing. The advantages of nonvolatility, higher data processing speed, lower power consumption and scalability hold the promise of the popularity of STT-MRAM in the future, of which spin transfer torque (STT) effect is the key. This thesis develops a spin diffusion model to study the spin dynamics in nanomagnetic structures and the corresponding STT effect acting on local magnetic moments. Chapter 2 provides an introduction to micromagnetic modeling, dominant magnetic interactions, and domain walls. Chapter 3 presents spin diffusion model, in which two approaches are discussed for handling the boundary conditions and we demonstrate their good performance in solving spin diffusion equation in finite element models. Chapter 3 also shows solutions for the spin accumulation in multi-layered magnetic structures at equilibrium and in dynamics. It also studies the case of spin transfer torque in magnetic nanostructures with the Néel wall, comparing it to the simplified Zhang & Li model. At the end of the chapter 3 we simulate the magnetization dynamics under STT effect using the FastMag micromagnetic simulation software coupled with the spin diffusion model.