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The interplay between interlayer coupling and exchange bias coupling in [NiFe/Mn] multilayerbased thin films was investigated by using ion-beam bombardment during deposition to control the configurations from superlattice to nanocomposite or hybrid-structured thin films. Results showed that well-defined interfaces in the superlattice [NiFe/Mn] thin film exhibited an interlayer coupling behavior. In contrast, an enhanced coercivity was observed in the nanocomposite [NiFe-Mn] thin film. However, the hybrid [NiFe-Mn]/[NiFe/Mn] thin film with an intermixed NiFeMn alloyed film component gave rise to unusual positive exchange bias coupling.

Thermal evolution of Co islands on Ag/Ge(111)-√3 × √3 and Ag/Si(111)-√3 × √3 surfaces was studied by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Ag-√3 × √3 buffer layer can avoid alloy formation of Co and Si or Ge below the annealing temperature 500 °C. The growth behavior of Co on Ag/Si(111)-√3 × √3 surfaces is very different from that on Ag/Ge(111)-√3 × √3 surfaces, although both the √3 structures can be classified as honeycomb chain trimer (HCT) model. Submonolayer Co on Ag/Si(111)-√3 × √3 surfaces prefer to form clusters below 500 °C. However, Co clusters nucleate and construct two-dimensional islands (2D islands) on Ag/Ge(111)-√3 × √3 surfaces after annealing to 300 °C. The result of different growth behavior comes from two major factors. One is antiphase boundaries (APBs) with extra electron states, which trap Co clusters on Ag/Si(111)-√3 × √3 surfaces. The other is the strong binding force that exists between Ge and Co atoms to cause the formation of Co period islands on Ag/Ge(111)-√3 × √3 surfaces. Copyright © 2008 John Wiley & Sons, Ltd.

We propose that macroscopic objects built from negative-permeability metamaterials may experience resonantly enhanced magnetic force in low-frequency magnetic fields. Resonant enhancement of the time-averaged force originates from magnetostatic surface resonances (MSR) which are analogous to the electrostatic resonances of negative-permittivity particles, well known as surface plasmon resonances in optics. We generalize the classical problem of MSR of a homogeneous object to include anisotropic metamaterials, and consider the most extreme case of anisotropy where the permeability is negative in one direction but positive in the others. It is shown that deeply subwavelength objects made of such indefinite (hyperbolic) media exhibit a pronounced magnetic dipole resonance that couples strongly to uniform or weakly inhomogeneous magnetic field and provides strong enhancement of the magnetic force, enabling applications such as enhanced magnetic levitation., 19 pages, 5 figures

We investigate the conditions under which single layer metamaterials may be described by bulk optical constants. Terahertz time domain spectroscopy is utilized to investigate two types of geometries, both with two different sizes of embedding dielectric---cubic and tetragonal unit cells. The tetragonal metamaterials are shown to yield layer dependent optical constants, whereas the cubic metamaterials yielded layer independent optical constants. We establish guidelines for when $\ensuremath{\epsilon}$ and $\ensuremath{\mu}$ can be used as material parameters for single layer metamaterials. Experimental results at terahertz frequencies are presented and supported by full wave three-dimensional electromagnetic simulations.

We present highly sub-wavelength magnetic metamaterials designed for operation at radio frequencies (RFs). A dual layer design consisting of independent planar spiral elements enables experimental demonstration of a unit cell size (a) that is ~ 700 times smaller than the resonant wavelength ({\lambda}0). Simulations indicate that utilization of a conductive via to connect spiral layers permits further optimization and we achieve a unit cell that is {\lambda}0/a ~ 2000. Magnetic metamaterials are characterized by a novel time domain method which permits determination of the complex magnetic response. Numerical simulations are performed to support experimental data and we find excellent agreement. These new designs make metamaterial low frequency experimental investigations practical and suggest their use for study of magneto-inductive waves, levitation, and further enable potential RF applications., Comment: 5 pages, 4 figures

We study interaction of the electromagnetic radiation with a series of thin film periodic nanostructures evolving from holes to islands. We show, through model calculations, simulations, and experiments, that the responses of these structures evolve accordingly, with two topologically distinct spectral types for holes and islands. We find also, that the response at the transitional pattern is singular. We show that the corresponding effective dielectric function follows the critical behavior predicted by the percolation theory and thus the hole-to-island structural evolution in this series is a topological analog of the percolation problem, with the percolation threshold at the transitional pattern.