In the first part of this thesis the fabrication and characterisation of vertical OSVs is described. The focus concerning the latter is on transport measurements carried out at low temperatures. The most important results were gained by the investigation of the Hanle and the TAMR effect. On the basis of all findings the physics behind the observed spin-valve effect can be unveiled. Thus, a complete and consistent model for the unambiguously tunneling-based MR is provided. Hereby, for the devices under investigation, a lot of open questions related to the MR in OSVs are answered. Furthermore, the RS effect was extensively studied in some of the structures. A key finding of these experiments is the observed interplay between the TAMR and RS. Also for the RS a fully consistent explanation is given, which is based on the modification of the La0.7Sr0.3MnO3 electrode’s oxygen stoichiometry. In the second part of the thesis the development of a new, shadow-evaporation-based fabrication process for lateral OSVs with a sub-100nm channel-length is presented. Preliminary results show that working devices are achieved which exhibit a large MR effect at room temperature.