Self-organization of confined dipolar particles in a parallel field.

Monte Carlo simulations of a Stockmayer fluid confined between two parallel walls are performed to investigate self-organization of magnetic nanocrystals in a field parallel to the walls as a function of density, field strength, and wall separation. In order to study the formation of mesoscopic structures, a large number of up to 12,000 particles have to be used. The particles organize into periodically spaced cylindrical-like columns whose width typically varies between 5 and 9 particle diameters at low density. At small heights the columns are quenched due to the parallel walls, while larger wall separations can accommodate several layers of columns in good agreement with experiments. An increase in density entails a clear increase in column thickness, whereas an increase in field strength seems to have the opposite effect.