Methods for magnetic recording are provided. The method can include: assembling a plurality of nanoparticles into a pattern on a disc; applying a polymer composition onto the pattern of nanoparticles; curing the polymer composition to form a polymer film on the disc, wherein the plurality of nanoparticles are immobilized in the pattern within the polymer film upon curing; and removing the polymer film containing the plurality of nanoparticles in the pattern. Diffraction gratings are also provided that can include a polymeric film comprising a plurality of nanoparticles immobilized in a pattern, wherein the polymer film defines a curvature.