The subject of this thesis is the study of cobalt nanowires self-assembled in a CeO2 matrix. The spontaneous self-assembly of nanowires occurs in strongly Co-doped CeO2 thin films grown by pulsed laser deposition. The metallic character of Co was attested by analysis of X-Ray absorption spectra taken at the Co K-edge. The formation of nanowires could be evidenced by transmission electron microscopy experiments (high resolution and energy filtered modes). Combining these results led to the conclusion of Co nanowires formation in the CeO2 matrix. The nanowires are oriented parallel to the growth direction; have length up to the thickness of film and have a narrow diameter size distribution centered in the 3 - 7 nm range. Due to the reduced values of diameter, these nanowires assemblies are model systems for studies in nanomagnetism. The magnetic properties of two nanowires assemblies (with diameters distribution centered on 3 and 5 nm) were investigated in details. The inner structure could be determined by means of transmission electron microscopy and the magnetization reversal was probed through static and dynamic magnetization measurements. Investigation of the magnetic anisotropy was carried out by analysis of resonance ferromagnetic spectra. The localization of the magnetization reversal was related to the inner structure of nanowires, more precisely to the orientation of hcp Co grains. In these grains, shape and magnetocrystalline anisotropies compete in strength and direction, leading to a thermally dependent effective anisotropy. The results presented indicate that it is possible to correlate the magnetic behavior with the real structure of wires in these systems.
