A5102732555- Physics of Superconductivity and Magnetism
- Crystallization and Solubility Studies
- X-ray Diffraction in Crystallography
- Advanced Condensed Matter Physics
- Magnetic properties of thin films
- Superconducting Materials and Applications
- Superconductivity in MgB2 and Alloys
- Magnetic and transport properties of perovskites and related materials
- Theoretical and Computational Physics
- Crystallography and molecular interactions
- Rare-earth and actinide compounds
- Iron-based superconductors research
- Magnetic Properties and Applications
- ZnO doping and properties
- High-pressure geophysics and materials
- Magnetism in coordination complexes
- Magnetic Properties of Alloys
- Metal complexes synthesis and properties
- Magnetic confinement fusion research
- Metal and Thin Film Mechanics
- Electronic and Structural Properties of Oxides
- Semiconductor materials and devices
- Metal-Organic Frameworks: Synthesis and Applications
- Quantum, superfluid, helium dynamics
- HVDC Systems and Fault Protection
Simon Fraser University
2012-2022
Burnaby Hospital
2017-2019
Oak Ridge National Laboratory
2003-2012
University of Canterbury
2012
University of Tennessee at Knoxville
2002-2011
University of Salford
1992-2000
University of Talca
1995-1998
Kuwait University
1995
Institute for Microstructural Sciences
1991-1993
University of Arkansas for Medical Sciences
1993
We report the realization of a microstructure which leads to very strong high-temperature flux pinning in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ crystals. Aligned discontinuous columns damaged material, about 50 \AA{} diameter and more than 15 \ensuremath{\mu}m long, are produced by 580-MeV Sn-ion irradiation. The enhancement is largest when applied magnetic field aligned with these tracks. At high temperatures fields much greater that random point defects, causes...
Crystallographic data, electrical and thermal transport measurements, magnetic susceptibility values are reported for several compounds alloys with the filled skutterudite structure, ${R}_{1\ensuremath{-}y}{\mathrm{Fe}}_{4\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{Sb}}_{12}$ ($R=\mathrm{La},$ Ce, or Th; $0<y<1;$ $x=0,$1). Room-temperature velocity of sound data is also reported. These materials interest because their potential in thermoelectric power generation refrigeration...
Structural, magnetic, electrical and thermal transport, heat-capacity measurements are reported on single crystals of ${\mathrm{Eu}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30},$ ${\mathrm{Sr}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30},$ ${\mathrm{Ba}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}.$ These compounds all crystallize in a cubic type-I ice clathrate structure, interest as potential thermoelectric materials. Neutron-diffraction were made crystal...
The development of biaxially textured, second-generation, high-temperature superconducting (HTS) wires is expected to enable most large-scale applications HTS materials, in particular electric-power applications. For many potential applications, high critical currents applied magnetic fields are required. It well known that columnar defects generated by irradiating materials with heavy ions significantly enhance the in-field current density. Hence, for over a decade scientists world-wide...
Flux pinning in Y-Ba-Cu-O crystals is studied as a function of fluence 3-MeV protons, which create random local defects. Order-of-magnitude increases the critical current density are deduced from magnetic hysteresis loops, with values up to 2\ifmmode\times\else\texttimes\fi{}${10}^{5}$ A/${\mathrm{cm}}^{2}$ observed at 77 K and 1 T. However, irreversibility line field-temperature plane potentials flux-creep studies hardly changed. These results compared melting models.
We demonstrated short segments of a superconducting wire that meets or exceeds performance requirements for many large-scale applications high-temperature materials, especially those requiring high supercurrent and/or engineering critical current density in applied magnetic fields. The these varied were met 3-micrometer-thick YBa2Cu3O(7-delta) films epitaxially grown via pulsed laser ablation on rolling assisted biaxially textured substrates. Enhancements the self-field as well excellent...
Ferromagnetic Mn5Ge3 thin films were grown on Ge(111) with solid-phase epitaxy. The epitaxial relationship between the alloy film and substrate is Mn5Ge3(001)//Ge(111) [100]Mn5Ge3//[11̄0]Ge. exhibit metallic conductivity strong ferromagnetism up to Curie temperature, TC=296 K. These are promising candidates for germanium-based spintronics.
Large enhancements in the critical current density Jc were produced single crystals of high-temperature superconductor Bi2Sr2Ca1Cu2O8 by irradiation with high energy Sn ions. In addition, irreversibility line was moved to considerably higher magnetic fields. contrast analogous studies on Y1Ba2Cu3O7, there little, if any, selective pinning when magnetizing field applied parallel linear, ion-damage-produced tracks.
${\mathrm{Cd}}_{2}{\mathrm{Os}}_{2}{\mathrm{O}}_{7}$ crystallizes in the pyrochlore structure and undergoes a metal-insulator transition (MIT) near 226 K. We have characterized MIT using x-ray diffraction, resistivity at ambient high pressure, specific heat, magnetization, thermopower, Hall coefficient, thermal conductivity. Both single crystals polycrystalline material were examined. The is accompanied by no change crystal symmetry unit-cell volume of less than 0.05%. shows little...
Pulsed-laser deposition was used to synthesize artificially layered high-temperature superconductors. Thin-film compounds were formed when the constraint of epitaxy stabilize SrCuO 2 -BaCuO superlattices in infinite layer structure. Using this approach, two new structural families, Ba Sr n –1 ,Cu +1 O +2+δ and 4 Cu +3 +6+δ , have been synthesized; these families superconduct at temperatures as high 70 kelvin.
Composite tapes of the superconductor Bi2Sr2CaCu2O8 on silver were irradiated with energetic light ions (0.8 GeV protons), creating extended splayed tracks ∼7 nm in diameter via fission Bi nuclei. Magnetic hysteresis indicates large enhancements persistent currents J, especially at high fields and temperatures, substantial expansion irreversible regime. The technique may be suitable for scale applications due to long range (∼half meter) fast protons.
We map a pinning boundary in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ crystals with columnar defects via (i) finite large drop of the persistent current J(T), (ii) maximum thermal relaxation rate S(T), and (iii) onset 1/H field dependence J(H). This is consistent ``accommodation'' ${\mathit{B}}^{\mathrm{?}}$(T) proposed by Nelson Vinokur, separating regime vortices well localized on pins from interaction-dominated collective...
Magnetically aligned samples of sintered ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ were used to test the effects oxygen-deficiency \ensuremath{\delta} (with \ensuremath{\delta}\ensuremath{\le}0.2) on superconductive magnetization M, critical current density ${\mathit{J}}_{\mathit{c}}$, irreversibility field ${\mathit{B}}_{\mathrm{irr}}$, upper ${\mathit{H}}_{\mathit{c}2}$, coherence length \ensuremath{\xi}, condensation...
Superconducting MgB2 films with Tc=38.6 K were prepared using a precursor-deposition, ex situ postprocessing approach. Precursor of boron, ∼0.5 μm thick, deposited onto Al2O3 (102) substrates by electron-beam evaporation; postanneal at 890 °C in the presence bulk and Mg metal produced highly crystalline films. X-ray diffraction indicated that exhibit some degree c-axis alignment, but are randomly oriented plane. Transport current measurements superconducting properties show high values...
We have studied the magnetic and magnetotransport properties of Mn-doped Ge grown by molecular-beam epitaxy. This group-IV dilute ferromagnetic semiconductor exhibits two transitions. An upper critical temperature TC* (∼112K for x∼0.05) is evident from extrapolated Curie–Weiss susceptibility Arrott plot analysis anomalous Hall effect data. The existence a lower TC (∼12K established ac data are fully compatible with bound polarons or clusters below which percolate at TC⪡TC*.
Temperature-dependent critical current density and normalized flux-creep rate, together with the dependence of vortex pinning energy, were studied in as-grown proton-irradiated Y-Ba-Cu-O crystals. A consistent interpretation is found within collective-pinning or vortex-glass models.
We present a comprehensive study of ferromagnetism and magnetotransport in Mn-doped germanium, grown with molecular-beam epitaxy. Ferromagnetism ${\mathrm{Mn}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}$ $(0<x<0.09)$ is characterized by two different ordering temperatures ${T}_{C}$ ${T}_{C}^{*}$ ${T}_{C}⪡{T}_{C}^{*}$. The onset global ferromagnetic order at coincides the percolation threshold for (activated) charge transport. Magnetism between originates from ``clustered dopants'' associated...
NMR measurements in solid ${\mathrm{H}}_{2}$ at low ortho concentrations between 0.4 and 4.2\ifmmode^\circ\else\textdegree\fi{}K show that the equilibrium distribution of molecules lattice is temperature dependent approached approximately exponentially time a given temperature. It suggested rearrangement process occurs by means ortho-para interchange.
The Ru(III) complexes indazolium [trans-RuCl4(1H-indazole)2] (KP1019) and sodium (NKP-1339) are leading candidates for the next generation of metal-based chemotherapeutics. Trifluoromethyl derivatives these compounds their imidazole pyridine analogues were synthesized to probe effect ligand lipophilicity on pharmacological properties types complexes. Addition CF3 groups also provided a spectroscopic handle 19F NMR studies exchange processes protein interactions. lipophilicities...
The time dependence of the irreversible superconductive magnetization (flux creep) has been studied in a high-${\mathit{J}}_{\mathit{c}}$, proton-irradiated ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{x}}$ single crystal for long periods, up to 3.5\ifmmode\times\else\texttimes\fi{}${10}^{5}$ s. A nonlogarithmic decay M with was observed. This deviation from conventional logarithmic not an approach system equilibrium state. fits extremely well...
We show that magnetic properties of clean superconductors with a large Ginzburg-Landau parameter \ensuremath{\kappa} at low temperatures are affected by the nonlocality microscopic current-field relation and can be described modified London equations. argue for materials temperatures, standard formula reversible magnetization in intermediate fields, M\ensuremath{\sim}ln(${\mathit{H}}_{\mathit{c}2}$/B), should contain field...