In an assembly of highly concentrated magnetic nanoparticles (NPs), the materials’ magnetic properties can be greatly influenced by their mutual dipolar interactions. In particular, the existence of a long-range ordered state where their individual magnetic moments are aligned ferromagnetically (dipolar superferromagnetic state, SFM) is predicted [1]. However, a clear-cut experimental evidence of it in real 3D NP assemblies has so far remained elusive. This is most likely due to the stringent geometrical/physical conditions required for inducing a dipolar SFM state. In this context, we intend to produce a dipolar SFM state in columnar supercrystals of dodecanoic acid coated Co NPs. This presentation focuses on the synthesis and characterizations of Co nanoparticles [2] and in the elaboration of mesostructures (labyrinths, voids and columns) obtained by the evaporation of a colloidal solution under an external magnetic field [3,4]. (1) Majetich, S. A.; Sachan, M. J. Phys. Appl. Phys. 2006, 39 (21), R407. (2) Lisiecki, I.; Pileni, M. P. Langmuir 2003, 19 (22), 9486. (3) Salzemann, C.; Richardi, J.; Lisiecki, I.; Weis, J.-J.; Pileni, M. P. Phys. Rev. Lett. 2009, 102 (14). (4) Germain, V.; Richardi, J.; Ingert, D.; Pileni, M. P. J. Phys. Chem. B 2005, 109 (12), 5541.