Interaction effects within Langmuir layers and three-dimensional arrays of ε-Co nanoparticles

Magnetostatic interactions are studied in two types of nanoparticle assemblies. Highly ordered monolayers of epsilon-Co nanoparticles are prepared from Langmuir films and self-assembled three-dimensional (3D) arrays formed by slow precipitation of colloidal dispersions of same nanoparticles. The structure of assemblies is found from electron microscopy and small-angle x-ray scattering. The differences in magnetic behavior are interpreted in terms of the particle moment, interparticle separation, and coordination number. Preferential in-plane magnetization is observed due to interactions within a monolayer. 3D arrays show stronger interactions compared to monolayers due to an increased number of nearest neighbors. (C) 2006 American Institute of Physics.