This book is a printed version of my PhD thesis in the Applied Physics Department of Cornell University under the supervision of Prof. Robert A. Buhrman and Prof. Daniel C. Ralph. A wide range of topics from the magnetoresistance behaviour of constrained domain walls to spin-transfer phenomenon in nanomagnets with special surface treatments are presented. The details of the device fabrication strategies used and the analytical material characterization techniques, including scanning transmission electron microscopy, electron energy loss spectroscopy and x-ray photoemission spectroscopy,...