Mon, 07 Jul 2008 00:31:01 BST CiteULike: di dchen Fischer http://www.citeulike.org/user/dchen/author/Fischer CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/dchen/article/2766831 <i>Physical Review Letters, Vol. 100, No. 14. (2008)</i><br /><br />We investigate the collective organization of paramagnetic colloidal particles externally driven above the periodic stripes of a uniaxial ferrimagnetic garnet film. An external field modulation induces vibration of the stripe walls and produces random motion of the particles. Defects in the stripe pattern break the symmetry of the potential and favor particle nucleation into large clusters above a critical density. Mismatch between particle size and pattern wavelength generates assemblies with different morphological order. At even higher field strengths, repulsive dipolar interactions between the particles induce cluster melting. We propose a novel approach to generate and externally control a variety of colloidal assemblies. Colloidal Assembly on Magnetically Vibrated Stripes Pietro Tierno Thomas Fischer Tom Johansen Francesc Sagués doi:10.1103/PhysRevLett.100.148304 Physical Review Letters, Vol. 100, No. 14. (2008) 2008-05-07T15:36:01-00:00 2008 Physical Review Letters 100 14 APS clusters colloids magnetic http://www.citeulike.org/user/dchen/article/943558 <i>Physical Review Letters, Vol. 97, No. 17. (2006)</i><br /><br />A light beam changes direction as it enters a liquid at an angle from another medium, such as air. Should the liquid contain molecules that lack mirror symmetry, then it has been predicted by Fresnel that the light beam will not only change direction, but will actually split into two separate beams with a small difference in the respective angles of refraction. Here we report the observation of this phenomenon. We also demonstrate that the angle of reflection does not equal the angle of incidence in a chiral medium. Unlike conventional optical rotation, which depends on the path-length through the sample, the reported reflection and refraction phenomena arise within a few wavelengths at the interface and thereby suggest a new approach to polarimetry that can be used in microfluidic volumes. Chiral Molecules Split Light: Reflection and Refraction in a Chiral Liquid Ambarish Ghosh Peer Fischer doi:10.1103/PhysRevLett.97.173002 Physical Review Letters, Vol. 97, No. 17. (2006) 2006-11-14T23:28:28-00:00 2006 Physical Review Letters 97 17 APS 2006 cool focus liquid material optical http://www.citeulike.org/user/dchen/article/2754251 <i>Physical Review Letters, Vol. 98, No. 18. (2007)</i><br /><br />Magnetic transmission x-ray microscopy is used to directly visualize the influence of a spin-polarized current on domain walls in curved permalloy wires. Pulses of nanosecond duration and of high current density up to 1.0×1012 A/m2 are used to move and to deform the domain wall. The current pulse drives the wall either undisturbed, i.e., as composite particle through the wire, or causes structural changes of the magnetization. Repetitive pulse measurements reveal the stochastic nature of current-induced domain-wall motion. Direct Imaging of Stochastic Domain-Wall Motion Driven by Nanosecond Current Pulses Guido Meier Markus Bolte René Eiselt Benjamin Krüger Dong Kim Peter Fischer doi:10.1103/PhysRevLett.98.187202 Physical Review Letters, Vol. 98, No. 18. (2007) 2008-05-04T16:33:53-00:00 2007 Physical Review Letters 98 18 APS 2007 focus magnetic material http://www.citeulike.org/user/dchen/article/2563145 <i>Physical Review Letters, Vol. 98, No. 2. (2007)</i><br /><br />Paramagnetic particles in a liquid above a solid dynamically self-assemble into two-dimensional (2D) viscoelastic clusters in a precessing magnetic field if the precession angle exceeds the magic angle. Hexagonal clusters rotate with a frequency proportional to the precession frequency of the magnetic field. The rotation is explained by viscoelastic shear waves excited in the clusters that can be visualized slightly above the magic angle. The cluster rotation and the visualization of viscoelastic modes are independent techniques to probe the rheological properties of the cluster. We find agreement between both techniques when determining the 2D cluster viscosity c10-11 N s/m. Viscoelasticity of Dynamically Self-Assembled Paramagnetic Colloidal Clusters Pietro Tierno Ramanathan Muruganathan Thomas Fischer doi:10.1103/PhysRevLett.98.028301 Physical Review Letters, Vol. 98, No. 2. (2007) 2008-03-19T17:16:50-00:00 2007 Physical Review Letters 98 2 APS 2007 cluster colloids magnetic