Olympic ring formation from newly prepared barium hexaferrite nanoparticle suspension

We report here, the first observation of features such as the Olympic Rings on transmission electron micrographs of amorphous BaFe₁₂O₁₉ nanoparticles prepared by a sonochemical decomposition technique. The barium hexaferrite was formed as a colloidal solution without the use of a surfactant. Rings of smaller dimensions trapped inside the larger ones was another unique observation. The intersection of two rings is amazing, as this is in direct contradiction to the proposed mechanism for the ring formation, based on the dry hole formation on an evaporating thin film completely wetted to the substrate. The creation of this unique feature is attributed to the interplay of magnetic forces with the regular particle-substrate interactions.