Localization and interaction effects in CdTeBi superlattices

The transport properties of CdTeBi superlattice have been measured as a function of the modulation wavelength. A logarithmic dependence with temperature was observed for the resistance at low temperature. The resistivity varied from 0.1 to 3.9 mΩcm at 1.7 K as the modulation wavelength varied from 177 to 81 A. A logarithmic behavior with H was observed for the transverse (longitudinal) magnetoresistance for low (high) fields. Samples were studied at temperatures down to 1.7 K and in magnetic fields up to 5 Tesla. No negative magnetoresistance as predicted by weak localization theory was observed. Hall coefficient measurements showed a logarithmic dependence with temperature which is indicative of Coulomb correlation effects (interaction theory). All measurements indicate that the transport behavior of CdTeBi superlattices is dominated by spin-orbit and/or interaction effects while weak localization plays a minimal role.     

Neutron diffraction analysis of a compositionally modulated alloy of nickel-copper

A compositionally modulated Ni_0.4Cu_0.6 alloy, made in a thin film of 1.8 μm thickness, was examined by polarized neutron diffraction. The results show that the material is ferromagnetic, with a large enhancement of the magnetic moment (0.3μ_B/Ni) with respect to a disordered alloy. The behaviour of the magnetic moments gives strong evidence of chemical clustering.     

Silver‐coated inverse opals formed from polystyrene spheres for surface‐enhanced Raman scattering

We have developed a new substrate for surface‐enhanced Raman scattering (SERS) measurements involving a thin silver layer deposited over an ion‐etched TiO₂ inverse opal. The latter is formed by chemically infiltrating a polystyrene opal array with TiO₂ followed by a thermal decomposition of the spheres. The SERS response of the these substrates is examined for several sphere sizes and lasers wavelengths; the results show that such substrates yield high enhance factors, comparable to substrates involving a silver layer deposited directly on a polystyrene opal array. Copyright © 2010 John Wiley & Sons, Ltd.     

Micromagnetic simulations of absoption spectra

Further development of a previously introduced method for numerically simulating magnetic spin waves is presented. Together with significant improvements in speed, the method now allows one to calculate the energy absorbed by the various modes excited by a position- and time-dependent H₁ field in a ferromagnetic body of arbitrary shape in the presence of a (uniform or non-uniform) static H₀ field as well as the internal exchange and anisotropy fields. The method is applied to the case of the single vortex state in a thin disc, a ring, and various square slabs, for which the absorption spectra are calculated and the most strongly excited resonance modes are identified.