Nanocomposite materials which associate inorganic nanoparticles and polymers with a high degree of organization are highly interesting for their applications in visible light optics (reflectors and guides) and hyper-frequencies (antennae and switches). We focus our study on a complex system combining self-organization of a diblock copolymer A-B and orientation properties under magnetic field of inorganic magnetic nanoparticles. We present here an experimental protocol for the synthesis by Atom Transfer Radical Polymerization (ATRP) of the symmetrical poly(n-butylmethacrylate)-b–poly(styrene) diblock copolymer (PBMA-b-PS) with high molar masses (about 100 000 g/mol). After spin-coating on a flat substrate (float glass, silicone or alumina) from a solution in a volatile solvent and annealing above the glass temperature, a thin film of such well-defined symmetrical diblocks are expected to self-organize into a lamellar (smectic type) order. The second component of the system consists in nanoparticles made of either superparamagnetic maghemite oxide Γ-Fe2O3 (soft magnets) or ferrimagnetic cobalt ferrite CoO.Fe2O3 (strong magnets). We are working on the proper dispersion of these nanoparticles within the PS blocks in order to obtain “sandwiches” made of magnetic thin layers alternating with the lamellae of the copolymer matrix. Optical Reflection Interference Contrast Microscopy (RICM) is convenient and fast to measure the thickness of the films (from a number of fringes) directly on their substrate and to detect characteristic defects of the long-range organization of the films (like holes). High resolution microscopies such as AFM and TEM will enable to measure the lamellar period but require to prepare thin films cross-sections.