Organic materials have great application potential in the field of spintronic devices, since pure organic layers or organic layers with embedded magnetic nanoparticles can be used to mediate or control a spin-polarized signal. In vertical spin valves, besides the intrinsic spin-transport properties of the organic layer, the magnetic properties of the magnetic electrode deposited onto it are determinant for the device performance. In devices containing mixed organic / metal layers, the large reported magneto-resistance is ascribed to the magnetization of the magnetic nanoparticles corroborated with the presence of a spin-dependent transport via the organic molecules. This lecture presents a systematic investigation of the influence of the molecular structure of organic molecules on the formation of transition metal nanoparticles in such organic matrices by co-evaporation in vacuum, on one hand, and on the growth of a transition metal electrode deposited on top of an organic layer, on the other hand. The structural properties of the heterostructures are assessed by means of transmission electron microscopy and atomic force microscopy. The electronic and magnetic properties are investigated by photoelectron spectroscopy and SQUID measurements, respectively. In addition the energy dispersion of the magneto-optical response of the systems is investigated experimentally by magneto-optical Kerr effect spectroscopy in the near infrared to ultraviolet spectral range and the results are compared to spectra simulated for multilayer systems to extract information about the interfacial chemistry.