Nanoscience and Nanotechnology Commons^™

Superheating Field In Superconductors With Nanostructured Surfaces, W. P. M. R. Pathirana, A. Gurevich

Physics Faculty Publications

We report calculations of a dc superheating field H_sh in superconductors with nanostructured surfaces. Numerical simulations of the Ginzburg-Landau (GL) equations were performed for a superconductor with an inhomogeneous impurity concentration, a thin superconducting layer on top of another superconductor, and superconductor-insulator-superconductor (S-I-S) multilayers.The superheating field was calculated taking into account the instability of the Meissner state with a nonzero wavelength along the surface, which is essential for realistic values of the GL parameter κ. Simulations were done for the materials parameters of Nb and Nb₃Sn at different values of κ and the mean free paths. We …

Dynamic Transition Of Vortices Into Phase Slips And Generation Of Vortex-Antivortex Pairs In Thin Film Josephson Junctions Under Dc And Ac Currents, Ahmad Sheikhzada, Alex Gurevich

Physics Faculty Publications

We present theoretical and numerical investigations of vortices driven by strong dc and ac currents in long Josephson junctions described by a nonlinear integro-differential equation which takes into account nonlocal electrodynamics of films, vortex bremsstrahlung, and Cherenkov radiation amplified by the attraction of vortices to the edges of the junction. This work focuses on the dynamics of vortices in Josephson junctions in thin films where the effects of Josephson nonlocality are essential but London screening is negligible. We obtained an exact solution for a vortex driven by an arbitrary time-dependent current in an overdamped junction where the vortex turns into …

Maximum Screening Fields Of Superconducting Multilayer Structures, Alex Gurevich

Physics Faculty Publications

It is shown that a multilayer comprised of alternating thin superconducting and insulating layers on a thick substrate can fully screen the applied magnetic field exceeding the superheating fields H_sof both the superconducting layers and the substrate, the maximum Meissner field is achieved at an optimum multilayer thickness. For instance, a dirty layer of thickness ~0.1μm at the Nb surface could increase H_s similar or equal to 240 mT of a clean Nb up to H_s similar or equal to 290 mT. Optimized multilayers of Nb₃Sn, NbN, some of the iron pnictides, or alloyed …

Synthesis Of Mild–Hard Aao Templates For Studying Magnetic Interactions Between Metal Nanowires, Jin-Hee Lim, Aurelian Rotaru, Seong-Gi Min, Leszek Malkinski, John B. Wiley

Physics Faculty Publications

The sequential application of mild and hard anodization techniques in the fabrication of porous aluminamembranes allows one to decrease the number of continuous pores in anodized aluminium oxide (AAO) templates. Initially, standard mild anodization techniques were used to create porous templates with 100 nm interpore distances and 70 nm pore diameters. Hard anodization treatment on the same membrane then produced interpore distances of about 265 nm with diameters of 110 nm. At the interface between the two anodization steps, many of the mild-side pores were terminated to create a mild–hard membrane (Mi–Ha AAO) where the functional interpore distances were 200–300 …

Microwave Absorption Of Patterned Arrays Of Nanosized Magnetic Stripes With Different Aspect Ratios, Leszek M. Malkinski, Minghui Yu, Andriy Y. Voyk, Donald J. Scherer Ii, Leonard Spinu, Weillie Zhou, Scott Whittenburg, Zachary Davis, Jin-Seung Jung

Physics Faculty Publications

Arrays consisting of nanosized stripes of Permalloy with different length-to-width ratios have been fabricated using electron beam nanolithography, magnetron sputtering, and lift-off process. These stripes have a thickness of 100 nm, a width of 300 nm, and different lengths ranging from 300 nm to 100 μm. The stripes are separated by a distance of 1 μm. Magnetization hysteresis loops were measured using a superconducting quantum interference device susceptometer. Microwave absorption at 9.8 GHz was determined by means of ferromagnetic resonance technique. The dependence of the resonant field on the angle between the nanostructure and the in-plane dc magnetic …

Cofe2o4 Nanostructures With High Coercivity, J S. Jung, J H. Lim, K H. Choi, S L. Oh, Y R. Kim, S H. Lee, D A. Smith, K L. Stokes, L Malkinski, C J. O'Connor

Physics Faculty Publications

Nanometer-sized ferrite magnetic materials are the subject of intense research interest due to their potential applications in high-density magnetic information storage. One of the most explored ferrite materials is the cobalt ferrite (CoFe2O4).. We have synthesized cobalt ferrite nanowires using cobalt ferrite nanoparticles in a porous anodic alumina template (AAT). The process of embedding ferrimagnetic particles into the pores was assisted by the magnetic field of a permanent magnet placed in vacuum directly under the substrate. Particles synthesized in the template were subsequently annealed at 600 °C for 2 h in Ar gas forming arrays of cobalt ferrite nanowires inside …

Magneto-Optical Spectra Of Closely Spaced Magnetite Nanoparticles, Damon Allen Smith, Yu A. Barnakov, B L. Scott, S A. White, Kevin L. Stokes

Physics Faculty Publications

The Faraday rotation spectrum of composites containing magnetite nanoparticles is found to be dependent on the interparticle spacing of the constituent nanoparticles. The composite materials are prepared by combining chemically synthesized Fe

3O4 smagnetited nanoparticles s8-nm diameterd and polysmethylmethacrylated . Composites are made containing a range of nanoparticle concentrations. The peak of the main spectral feature depends on nanoparticle concentration; this peak is observed to shift from approximately 470 nm for sdilute compositesd to 540 nm concentrated . We present a theory based on the discrete-dipole approximation which accounts for

optical coupling between magnetite particles. Qualitative correlations between theoretical calculations …

Ultrafine Nife2o4 Powder Fabricated From Reverse Microemulsion Process, Jiye Fang, Narayan Shama, Le Duc Tung, Eun Young Shin, Charles J. O'Connor, Kevin L. Stokes, Gabriel Caruntu, John B. Wiley, Leonard Spinu, Jinke Tang

Physics Faculty Publications

NiFe2O4 ultrafine powder with high crystallinity has been prepared through a reverse microemulsion route. The composition in starting solution was optimized, and the resulting NiFe2O4 was formed at temperature of around 550–600 °C, which is much lower than that observed from the solid-state reaction. Magnetic investigation indicates that samples are soft-magnetic materials with low coercivity and with the saturation magnetization close to the bulk value of Ni ferrite.

Self-Assembly Of Fept Nanoparticles Into Nanorings, Weilie L. Zhou, Jibao He, Jiye Fang, Tuyet-Anh Huynh, Trevor J. Kennedy, Kevin L. Stokes, Charles J. O'Connor

Physics Faculty Publications

The application of nanoparticles as quantum dots in nanoelectronics demands their arrangement in ordered arrays. Shape controlled self-assembly is a challenge due to the difficulties of obtaining proper self-assembling parameters, such as solvent concentration, organic ligands, and nanoparticle size. In this article, hard magnetic FePt nanoparticles were synthesized using a combination approach of reduction and thermal decomposition. The nanoparticles are about 4.5 nm and appeared as truncated octahedral enclosed by the

{100} and {111}

crystal facets of fcc structure. The nanoparticles are of hexagonal close packing and orient randomly in the self-assembly nanoarrays. By diluting the solution for large-area self-assembly, …

Synthesis And Magnetic Properties Of Copt–Poly(Methylmethacrylate) Nanostructured Composite Material, Jiye Fang, Kevin L. Stokes, Jibao He, Weillie L. Zhou, Charles J. O'Connor, Daniela Caruntu

Physics Faculty Publications

We have prepared nanometer-sized CoPt particles dispersed in a poly~methyl methacrylate~PMMA!matrix, as a novel nanostructured magnetic plastic, through a soft chemical processing route. In this work, CoPt nanoparticles were successfully synthesized from a solution phase reduction system in the presence of capping ligands and stabilizing agents at high temperature. The CoPt nanoparticles were annealed at 400 °C for 3 h, and were subsequently re-dispersed inmethylmethacrylate~monomer! . The polymerization was induced by a UV source and the hardness of final product was adjusted by varying the amount of monomeric cross-link agent. Annealed bare CoPt nanoparticles as a ‘‘core’’ material and CoPt–PMMA …