Ph.D. in Condensed Matter Physics and Nanotechnology, Physics Department, Faculty of Sciences, University of Porto, under the guidance of Professors Y. G. Pogorelov and J. P. Araújo (Univ. Porto) and Professor H. L. Gomes (Univ. Algarve). With the following thesis: Quantum Effects for Spintronic Device Optimization (unanimously approved, 2009). This work was supported by FCT through the fellowship: SFRH/BD/24190/2005.