CiteULike: dchen's magnetic

Measuring the Kinetics of Biomolecular Recognition with Magnetic Colloids

Cohen Tannoudji — 2008-05-07T23:01:32-00:00

Physical Review Letters, Vol. 100, No. 10. (2008)

We introduce a general methodology based on magnetic colloids to study the recognition kinetics of tethered biomolecules. Access to the full kinetics of the reaction is provided by an explicit measure of the time evolution of the reactant densities. Binding between a single ligand and its complementary receptor is here limited by the colloidal rotational diffusion. It occurs within a binding distance that can be extracted by a reaction-diffusion theory that properly accounts for the rotational Brownian dynamics. Our reaction geometry allows us to probe a large diversity of bioadhesive molecules and tethers, thus providing a quantitative guidance for designing more efficient reactive biomimetic surfaces, as required for diagnostic, therapeutic, and tissue engineering techniques.

Colloidal Assembly on Magnetically Vibrated Stripes

Pietro Tierno — 2008-05-07T15:36:01-00:00

Physical Review Letters, Vol. 100, No. 14. (2008)

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.

Spin Proximity Effect in Ultrathin Superconducting Be-Au Bilayers

XS Wu — 2008-05-05T16:25:55-00:00

Physical Review Letters, Vol. 96, No. 12. (2006)

We present a detailed study of the effects of interface spin-orbit coupling on the critical field behavior of ultrathin superconducting Be/Au bilayers. Parallel field measurements were made in bilayers with Be thicknesses in the range of d=2–30 nm and Au coverages of 0.5 nm. Though the Au had little effect on the superconducting gap, it produced profound changes in the spin states of the system. In particular, the parallel critical field exceeded the Clogston limit by an order of magnitude in the thinnest films studied. In addition, the parallel critical field unexpectedly scaled as Hc||/01/d, suggesting that the spin-orbit coupling energy was proportional to 0/d2. Tilted field measurements showed that, contrary to recent theory, the interface spin-orbit coupling induces a large in-plane superconducting susceptibility but only a very small transverse susceptibility.

Imaging Spin-Reorientation Transitions in Consecutive Atomic Co Layers on Ru(0001)

Farid Gabaly — 2008-05-05T16:10:21-00:00

Physical Review Letters, Vol. 96, No. 14. (2006)

By means of spin-polarized low-energy electron microscopy, we show that the magnetic easy axis of one to three atomic-layer thick cobalt films on Ru(0001) changes its orientation twice during deposition: One-monolayer and three-monolayer thick films are magnetized in plane, while two-monolayer films are magnetized out of plane. The Curie temperatures of films thicker than one monolayer are well above room temperature. Fully relativistic calculations based on the screened Korringa-Kohn-Rostoker method demonstrate that only for two-monolayer cobalt films does the interplay between strain, surface, and interface effects lead to perpendicular magnetization.

Direct Imaging of Stochastic Domain-Wall Motion Driven by Nanosecond Current Pulses

Guido Meier — 2008-05-04T16:33:53-00:00

Physical Review Letters, Vol. 98, No. 18. (2007)

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.

Multiferroicity Induced by Dislocated Spin-Density Waves

Joseph Betouras — 2008-05-04T00:09:06-00:00

Physical Review Letters, Vol. 98, No. 25. (2007)

We uncover a new pathway towards multiferroicity, showing how magnetism can drive ferroelectricity without relying on inversion symmetry breaking of the magnetic ordering. Our free-energy analysis demonstrates that any commensurate spin-density-wave ordering with a phase dislocation, even if it is collinear, gives rise to an electric polarization. Because of the dislocation, the electronic and magnetic inversion centers do not coincide, which turns out to be a sufficient condition for multiferroic coupling. The novel mechanism explains the formation of multiferroic phases at the magnetic commensurability transitions, such as the ones observed in YMn2O5 and related compounds. We predict that in these multiferroics an oscillating electrical polarization is concomitant with the uniform polarization. On the basis of our theory, we put forward new types of magnetic materials that are potentially ferroelectric.

Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange

G Binasch — 2008-05-03T20:09:10-00:00

Physical Review B, Vol. 39, No. 7. (1 March 1989), 4828.

Guiding superconducting vortices with magnetic domain walls

Vlasko Vlasov — 2008-05-03T16:28:20-00:00

Physical Review B (Condensed Matter and Materials Physics), Vol. 77, No. 13. (2008)

We demonstrate a unique prospect for inducing anisotropic vortex pinning and manipulating the directional motion of vortices by using the stripe domain patterns of a uniaxial magnetic film in the superconducting/ferromagnetic hybrid. Our observations can be described by a model, which considers interactions between magnetic charges of vortices and surface magnetic charges of domains resulting in the enhanced pinning of vortices on domain walls.

Viscoelasticity of Dynamically Self-Assembled Paramagnetic Colloidal Clusters

Pietro Tierno — 2008-03-19T17:16:50-00:00

Physical Review Letters, Vol. 98, No. 2. (2007)

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.