Magnetic assembly of gold core-shell necklace resonators

Gold core-shell necklace structures are assembled by inducing magnetic moments of gold-coated paramagnetic microspheres and a diamagnetic sphere using an external magnetic field. Sphere numbers in a necklace structure was tuned solely by controlling magnetic permeability of background medium. A necklace structure consisting of evenly spaced metal spheres or disks is known to be a good medium for a plasmonic resonance. Therefore, their optical properties were numerically studied. The electric field enhancement by a factor of 1800 was estimated in the gaps between adjacent spheres at a resonant wavelength. The wavelength-scaling strategies of our structures to visible wavelength are also discussed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4706254]