Fabrication of artificial crystals with tunable lattice constant via self-assembly of floating magnetic particles

We report stable ordered arrays of millimeter-size magnetic particles floating on a liquid surface. Self-assembly into a regular two-dimensional lattice results from lateral magnetic interactions between the particles. The lattice constant may be easily tuned by the application of external magnetic field. The array symmetry is designed by using different particle shapes, magnets, and magnet position inside the particle, so that complex symmetries may be achieved. Three-dimensional ordered arrays are obtained in a stack of containers with floating magnets. Computer simulations of electromagnetic wave propagation in such three-dimensional structures suggest an opening of a tunable photonic bandgap in the microwave range.