title: Pattern formation in a monolayer of magnetic spheres.
abstract: Pattern formation is investigated for a vertically vibrated monolayer of magnetic spheres. The spheres of diameter D encase cylindrical magnetic cores of length l. For large D/l, we find that the particles form a hexagonal-close-packed pattern in which the particles' dipole vectors assume a macroscopic circulating vortical pattern. For smaller D/l, the particles form concentric rings. The static configurational magnetic energy (which depends on D/l) appears to be a determining factor in pattern selection even though the experimental system is driven and dissipative.
authors.affiliation: Institute for Research in Electronics and Applied Physics, Department of Physics, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Stambaugh
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Lathrop
authors.forename: Edward
authors.initials: E
authors.lastname: Ott
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Losert