Planar magnetic colloidal crystals

We report a novel form of planar magnetic colloidal crystals formed by coat ed magnetic microspheres floating on a liquid meniscus. Under an external m agnetic field, the balance between the repulsive magnetic interaction and t he "attractive" interaction, due to the weight of the particles projected a long the surface tangent, yields not only the triangular lattice with a var iable lattice constant, but also all the other planar crystal symmetries su ch as the oblique, centered-rectangular, rectangular, and square lattices. By using two different sized magnetic particles, local formations of 2D qua sicrystallites with fivefold symmetry are also observed.