Peak effect in polycrystalline vortex matter

We report a study of the peak-effect phase diagram of a strongly disordered type-II superconductor V-21 at. %Ti using ac magnetic susceptibility and small-angle neutron scattering (SANS). In this system, the peak effect appears only at fields higher than 3.4 T. The sample is characterized by strong atomic disorder. Vortex states with field-cooled thermal histories show that both deep in the mixed state, as well as close to the peak effect, there exist no long-range orientationally ordered vortex lattices. The SANS scattering radial widths reveal vortex states ordered in the sub-mum scale. We conjecture that the peak effect in this system is a remnant of the Bragg glass disordering transition, but occurs on submicron length scales due to the presence of strong atomic disorder on larger length scales.     

Heterodyne detection of random Gaussian signals in the optical and infrared: optimization of pulse duration

The performance of a heterodyne system in estimating the mean intensity of a gaussian random signal depends on the mean number of photocarriers released by the signal radiation in its coherence volume (degeneracy parameter). In a pulsed radar, this parameter can be manipulated by varying the pulse duration while keeping the mean number of signal photocarriers constant. Furthermore, in a number of situations of practical interest, an optimal pulse duration exists, corresponding to a degeneracy parameter of unity. Heterodyne and direct detection are compared for this case, and direct detection is found to be superior in the strong-signal limit.     

Optical and electronic transport anisotropies in plastically deformed CdS

Measurements of polarized optical transmission and reflectivity in the region of the fundamental gap, as well as of the electrical conductivity of plastically deformed CdS were made to probe the electronic properties of this material. From the observed anisotropies in the d.c. electrical conductivity and in optical absorption, a model is suggested to explain the observed features in terms of dislocation energy bands.     

Superconducting transition in polysulfur nitride as a function of crystal quality

The superconducting transition temperature in polysulfur nitride crystals of various quality appears invariant between 0.26 and 0.28°K, but the completeness of the transition varies from sample to sample. A residual resistance remains in bulk samples which reflects the density of fiber segment junctions.     

Magnetic Fe doped ZnO nanofibers obtained by electrospinning

We demonstrate structural and room temperature magnetic properties of Fe doped ZnO nanofibers (NFs) obtained by electrospinning followed by calcination. The observed NFs, formed from crystalographically oriented, approximately 4.5?nm particles conglomerates, were approximately 200?nm in diameter. The reported synthesis of room temperature ferromagnetic Fe doped ZnO NFs is both facile and economical, and is therefore suggested as a generic method of fabricating biocompatible magnetic materials. The major substrates selected for the NFs synthesis (Zn, Fe) comprised of relatively low toxicity materials. Incorporating 10% Fe into ZnO does not modify the wurtzite crystal structure of the host material. No evidence of impurity phase was detected by either X-ray or electron diffraction. Magnetometry studies and Magnetic Force Microscopy imaging reveal a local ferromagnetic order that persists up to room temperature. We suggest that the observed phenomenon is either due to a mechanism mediated by presence of oxygen vacancies and/or is related to iron-rich precipitates.