Ordered structures with point-like defects of various shapes in magnetic fluid films

Owing to the increasing importance of the photonic crystals in opto-electronics, the fabrication of ordered structures becomes urgently required. In this work, we report the formation of the two-dimensional hexagonal ordered structure in the highly homogeneous magnetic fluid film when a magnetic field is applied perpendicularly to the film surface. Furthermore, we investigate the structural patterns when point-like defects of various shapes are introduced artificially into the film. It was found that, for the triangle or the hexagonal defects, a nearly perfect ordered structure is obtained around the defects in the magnetic fluid film, whereas twin boundaries exist for rectangular defects. The existence of the twin boundaries is attributed to the mismatch in the characterized angles of the rectangular defect (=90°) and the hexagonal ordered structure (=60°) in the magnetic fluid film. These observed results reveal the promising ordered structures for developing photonic-crystal cavities by using the magnetic fluid films with point-like cavities.