A5002541962- Physics of Superconductivity and Magnetism
- Iron-based superconductors research
- Superconducting Materials and Applications
- Superconductivity in MgB2 and Alloys
- Rare-earth and actinide compounds
- Corporate Taxation and Avoidance
- HVDC Systems and Fault Protection
- Intellectual Capital and Performance Analysis
- Magnetic and transport properties of perovskites and related materials
- Magnetic Properties and Applications
- Magnetic properties of thin films
- Advanced Condensed Matter Physics
- Magnetic Properties of Alloys
- Particle accelerators and beam dynamics
- Thermal Analysis in Power Transmission
- Chalcogenide Semiconductor Thin Films
- Theoretical and Computational Physics
- Surface and Thin Film Phenomena
- Layered Double Hydroxides Synthesis and Applications
- Advanced Materials Characterization Techniques
- Magneto-Optical Properties and Applications
- Advanced Combustion Engine Technologies
- Quantum, superfluid, helium dynamics
- High-pressure geophysics and materials
- Electrical Contact Performance and Analysis
Florida State University
2015-2024
National High Magnetic Field Laboratory
2015-2024
Beijing Forestry University
2022-2023
Southern University of Science and Technology
2022
Tallahassee Orthopedic Clinic
2019
Chinese Academy of Sciences
2011-2014
International Centre for Materials Physics
2011-2014
University of Wisconsin–Madison
1999-2011
Collaborative Innovation Center of Advanced Microstructures
2011
Nanjing University
1998-2011
We performed high-field magnetotransport and magnetization measurements on a single crystal of the 122-phase iron pnictide Ba(Fe1−xCox)2As2. Unlike high-temperature superconductor cuprates 1111-phase oxypnictides, Ba(Fe1−xCox)2As2 showed practically no broadening resistive transitions under magnetic fields up to 45 T. report temperature dependencies upper critical field Hc2 both parallel perpendicular c-axis, irreversibility Hirrc(T), rather unusual symmetric volume pinning force curve Fp(H)...
Less than two years after the discovery of high temperature superconductivity in oxypnictide LaFeAs(O,F) several families superconductors based on Fe layers (1111, 122, 11, 111) are available. They share characteristics with cuprate that compromise easy applications, such as layered structure, small coherence length, and unconventional pairing, On other hand Fe-based have metallic parent compounds, their electronic anisotropy is generally smaller does not strongly depend level doping,...
<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Development of high-field magnets using high temperature superconductors (HTS) is a core activity at the NHMFL. Magnet technology based on both YBCO-coated tape conductors and Bi-2212 round wires being pursued. Two specific projects are underway. The first user magnet with 17 T YBCO coil set which, inside an LTS outsert, will generate combined field 32 T. second 7 Bi2212 demonstration to be...
We show that despite the low anisotropy, strong vortex pinning, and high irreversibility field Hirr close to upper critical Hc2 of Ba(Fe1−xCox)2As2, current density Jgb across [001] tilt grain boundaries (GBs) thin film Ba(Fe1−xCox)2As2 bicrystals is strongly depressed, similar high-Tc cuprates. Our results suggest weak-linked GBs are characteristic both cuprates pnictides because competing orders, carrier density, unconventional pairing symmetry.
Multifilamentary Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sr CaCu O xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (Bi-2212) wire made by the powder-in-tube technique is only high-temperature superconductor in round shape preferred magnet builders. The critical current density (J xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> ) of Bi-2212 was improved significantly development overpressure heat treatment past few years....
A key issue affecting the critical current density of MgB2 is lack full electrical connectivity. In situ wires can be easily fabricated by reacting Mg powder with amorphous B powder, but such powders normally contain impurities as B2O3 a result exposure to air. Here we introduce practical method for removing prior making MgB2. X-ray diffraction and microstructure analysis show that results in decrease MgO from 5.3 1.5 mol% final reacted Normal state transport measurements using Rowell...
Early studies have found quasi-reversible magnetization curves in polycrystalline bulk rare-earth iron oxypnictides that suggest either wide-spread obstacles to intergranular current or very weak vortex pinning.In the present study of samarium and neodymium oxypnictide samples made by high pressure synthesis, hysteretic is significantly enhanced.Magneto optical imaging field dependence remanent as a function particle size both show global currents over whole sample do exist but intragranular...
We have recently shown that the gas present in only ~ 70% dense filaments of as-drawn Bi-2212 wire agglomerates into large bubbles fill entire filament diameter during melt phase heat treatment. Once formed, these never disappear, although they can be bridged by 2212 grains formed on cooling. In order to test effect critical current Ic, we increased density after drawing using 2 GPa cold isostatic pressure, finding bubble and size were greatly reduced Ic could at least doubled. conclude...
Most studies of Bi2Sr2CaCu2Ox (Bi2212) show that the critical current density Jc is limited by connectivity filaments, but what determines still elusive. Here we report on role played filament porosity in limiting Jc. By a microstructural investigation wires quenched from melt state, find unreacted wire agglomerates into bubbles segment Bi2212 within filaments discrete sections. These do not disappear during subsequent processing because they are only partially filled grains as forms...
Abstract Why Bi 2 Sr CaCu O x (Bi2212) allows high critical current density J c in round wires rather than only the anisotropic tape form demanded by all other temperature superconductors is important for future magnet applications. Here we compare local texture of state-of-the-art Bi2212 and Bi2223 ((Bi,Pb) Ca Cu 3 10 ), finding that wire generates a dominant -axis growth also enforces biaxial (FWHM <15°) while simultaneously allowing -axes its polycrystals to rotate azimuthally along...
High-temperature superconductors (HTS) could enable high-field magnets stronger than is possible with Nb-Ti and Nb3Sn, but two challenges have so far been the low engineering critical current density JE, especially in high-current cables, danger of quenches. Most HTS made out REBCO coated conductor. Here we demonstrate stable, reliable training-quench-free performance Bi-2212 racetrack coils wound a Rutherford cable fabricated from wires new precursor powder. These round multifilamentary...
An important predicted, but so far uncharacterized, property of the new superconductor MgB2 is electronic anisotropy arising from its layered crystal structure. Here we report on three c-axis oriented thin films, showing that upper critical field ratio Hc2par/Hc2perp 1.8 to 2.0, increasing with higher resistivity. Measurements magnetic field-temperature phase diagram show flux pinning disappears at H* ~ 0.8Hc2perp(T) in untextured samples. Hc2par(0) strongly enhanced by alloying 39 T for...
Increasing the critical current density (Jc) of multifilamentary round wire Ag/Bi2Sr2CaCu2Ox(2212) requires understanding its complicated microstructure, in which extensive bridges between filaments are prominent. In this first through-process quench study 2212 wire, we determined how microstructure develops during a standard partial-melt process and filament bridging occurs. We found that can bond together melt state. As starts to grow on subsequent cooling, observed two types form. One...
We report a direct current transport study of the local intergrain connections in polycrystalline SmFeAsO0.85 (Sm1111) bulk, for which we earlier estimated significant intergranular critical density Jc. Our combined low temperature laser scanning microscopy and electron observations revealed only few grain-to-grain paths, most switched off when magnetic field was applied. These regions typically occur where crosses Fe–As, is normal-metal wetting-phase that surrounds Sm1111 grains, producing...
Directional point-contact Andreev-reflection measurements in Ba(Fe(1-x)Co(x))2As2 single crystals (T(c) = 24.5 K) indicate the presence of two superconducting gaps with no line nodes on Fermi surface. The spectra also feature additional structures related to electron-boson interaction, from which characteristic boson energy Ω(b)(T) is obtained, very similar spin-resonance observed neutron scattering experiments. Both and can be reproduced within a three-band s ± Eliashberg model by using an...
Bi-2212 round wire is made by the powder-in-tube technique. An unavoidable property of conductors that there about 30% void space in as-drawn wire. We have recently shown gas present agglomerates into large bubbles and they are presently most deleterious current limiting mechanism. By densifying short 2212 wires before reaction through cold isostatic pressing (CIPping), was almost removed bubble density reduced significantly, resulting a doubled engineering critical (JE) 810 A/mm2 at 5 T,...
The grain boundaries (GBs) of high-temperature superconductors (HTSs) intrinsically limit the maximum achievable inter-grain current density (), when misalignment between crystallographic axes adjacent grains exceeds a certain value. A prominent effect resulting from large-angle GBs is hysteresis increasing and decreasing field branches. Here, we investigate this feature for K- Co-doped Ba-122 polycrystalline bulks with systematically varied size find that widely accepted explanation...