| A theoretical study of a three-dimensional (3D) N/S interface with arbitrary spin polarization and interface geometry is presented. The 3D model gives the same intrinsic spin polarization and superconducting gap dependence as the 1D model. This demonstrates that the 1D model can be use to t 3D data.;Using this model, a Heusler alloy is investigated. Andreev reflection measurements show that the spin polarization is 80% in samples sputtered on unheated MgO(100) substrates and annealed at high temperatures. However, the spin polarization is considerably smaller in samples deposited on heated substrates.;Ferromagnetic FexSi---x alloys have been proposed as potential spin injectors into silicon with a substantial spin polarization. Andreev Reflection Spectroscopy (ARS) is utilized to determine the spin polarization of both amorphous and crystalline Fe65Si 35 alloys. The amorphous phase has a significantly higher spin polarization than that of the crystalline phase.;In this thesis, (1111) Fe SmO0:82F0:18FeAs and Pb superconductors are used to measure the spin polarization of a highly spin-polarized material, La0:67Sr0:33MnO3. Both materials yield the same intrinsic spin polarization, therefore, Fe-superconductors can be used in ARS. Based on the behavior of the differential conductance for highly spin polarized LSMO and small polarization of Au, it can be concluded that the Fe-Sc is not a triplet superconductor.;Zero bias anomaly (ZBA), in point contact Andreev reflection (PCAR), has been utilized as a characteristic feature to reveal many novel physics. Complexities at a normal metal/superconducting interface often cause nonessential ZBA-like features, which may be mistaken as ZBA. In this work, it is shown that an extrinsic ZBA, which is due to the contact resistance, cannot be suppressed by a highly spin-polarized current while a nonessential ZBA cannot be affected the contact resistance.;Finally, Cu/Cu multilayer GMR structures were fabricated and the GMR% measured at 300 K and 4.5 K gave responses of 63% and 115% respectively. Not only do the GMR structures have a large enhancement of resistance, but by applying an external magnetic field it is shown that, unlike most materials, the spin polarization can be tuned to values of 0.386 to 0.415 from H = 0 kOe to H = 15 kOe. |
