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Search Results: 1 - 10 of 448682 matches for " J. L. MacManus-Driscoll "
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Strong Pinning Enhancement in MgB2 Using Very Small Dy2O3 Additions
S. K. Chen,M. Wei,J. L. MacManus-Driscoll
Physics , 2006, DOI: 10.1063/1.2203209
Abstract: 0.5 to 5.0 wt.% Dy2O3 was in-situ reacted with Mg + B to form pinned MgB2. While Tc remained largely unchanged, Jc was strongly enhanced. The best sample (only 0.5 wt.% Dy2O3) had a Jc of 6.5 x 10^5 A/cm^2 at 6K, 1T and 3.5 x 10^5 A/cm^2 at 20K, 1T, around a factor of 4 higher compared to the pure sample, and equivalent to hot-pressed or nano-Si added MgB2 at below 1T. Even distributions of nano-scale precipitates of DyB4 and MgO were observed within the grains. The room temperature resistivity decreased with Dy2O3 indicative of improved grain connectivity.
Practical vortex diodes from pinning enhanced YBa2Cu3O7-d
S. A. Harrington,J. L. MacManus-Driscoll,J. H. Durrell
Physics , 2009, DOI: 10.1063/1.3182735
Abstract: We identify a scalable, practical route to fabricating a superconducting diode. The device relies for its function on the barrier to flux vortex entry being reduced at the substrate interface of a superconducting pinning enhanced YBa2Cu3O7-d nano-composite film. We show that these composite systems provide a practical route to fabricating a useful superconducting diode and demonstrate the rectification of an alternating current.
Strong influence of boron precursor powder on the critical current density of MgB2
S. K. Chen,K. A. Yates,M. G. Blamire,J. L. MacManus-Driscoll
Physics , 2005, DOI: 10.1088/0953-2048/18/11/011
Abstract: The influence of the nature of the boron precursor on the superconducting properties of polycrystalline MgB2 was studied. Critical current densities for the MgB2 made from high purity amorphous boron are at least a factor of three higher than typical values measured for standard MgB2 samples made from amorphous precursors. Two possible mechanisms are proposed to account for this difference. Samples made from crystalline boron powders have around an order of magnitude lower Jc compared to those made from amorphous precursors. X-ray, Tc and resistivity studies indicate that this is as a result of reduced current cross section due to the formation of Mg-B-O phases. The samples made from amorphous B contain far fewer Mg-B-O phases than crystalline B despite the fact that the amorphous B contains more B2O3. The different reactivity rates of the precursor powders accounts for this anomaly.
Improved Current Densities in MgB2 By Liquid-Assisted Sintering
S. K. Chen,Z. Lockman,M. Wei,B. A. Glowacki,J. L. MacManus-Driscoll
Physics , 2005, DOI: 10.1063/1.1947374
Abstract: Polycrystalline MgB2 samples with GaN additions were prepared by reaction of Mg, B, and GaN powders. The presence of Ga leads to a low melting eutectic phase which allowed liquid phase sintering and produces plate-like grains. For low-level GaN additions (5% at. % or less), the critical transition temperature, Tc, remained unchanged and in 1T magnetic field, the critical current density, Jc was enhanced by a factor of 2 and 10, for temperatures of \~5K and 20K, respectively. The values obtained are approaching those of hot isostatically pressed samples.
Normal state properties of high angle grain boundaries in (Y,Ca)Ba2Cu3O7-delta
S. H. Mennema,J. H. T. Ransley,G. Burnell,J. L. MacManus-Driscoll,E. J. Tarte,M. G. Blamire
Physics , 2004, DOI: 10.1103/PhysRevB.71.094509
Abstract: By lithographically fabricating an optimised Wheatstone bridge geometry, we have been able to make accurate measurements of the resistance of grain boundaries in Y1-xCaxBa2Cu3O7-d between the superconducting transition temperature, Tc, and room temperature. Below Tc the normal state properties were assessed by applying sufficiently high currents. The behaviour of the grain boundary resistance versus temperature and of the conductance versus voltage are discussed in the framework charge transport through a tunnel barrier. The influence of misorientation angle, oxygen content, and calcium doping on the normal state properties is related to changes of the height and shape of the grain boundary potential barrier.
Benefits of current percolation in superconducting coated conductors
N. A. Rutter,J. H. Durrell,M. G. Blamire,J. L. MacManus-Driscoll,H. Wang,S. R. Foltyn
Physics , 2005, DOI: 10.1063/1.2093920
Abstract: The critical currents of MOD/RABiTS and PLD/IBAD coated conductors have been measured as a function of magnetic field orientation and compared to films grown on single crystal substrates. By varying the orientation of magnetic field applied in the plane of the film, we are able to determine the extent to which current flow in each type of conductor is percolative. Standard MOD/RABiTS conductors have also been compared to samples whose grain boundaries have been doped by diffusing Ca from an overlayer. We find that undoped MOD/RABiTS tapes have a less anisotropic in-plane field dependence than PLD/IBAD tapes and that the uniformity of critical current as a function of in-plane field angle is greater for MOD/RABiTS samples doped with Ca.
A new kind of vortex pinning in superconductor / ferromagnet nanocomposites
A. Palau,H. Parvaneh,N. A. Stelmashenko,H. Wang J. L. Macmanus-Driscoll,M. G. Blamire
Physics , 2006, DOI: 10.1088/0953-2048/20/9/S04
Abstract: This paper reports the observation of hysteresis in the vortex pinning in a superconductor / ferromagnetic epitaxial nanocomposite consisting of fcc Gd particles incorporated in a Nb matrix. We show that this hysteretic pinning is associated with magnetic reversal losses in the Gd particles and is fundamentally different in origin to pinning interactions previously observed for ferromagnetic particles or other microstructural features.
Strongly Enhanced Current Densities in Superconducting Coated Conductors of YBa2Cu3O7-x + BaZrO3
J. L. MacManus-Driscoll,S. R. Foltyn,Q. X. Jia,H. Wang,A. Serquis,L. Civale,B. Maiorov,M. E. Hawley,M. P. Maley,D. E. Peterson
Physics , 2004, DOI: 10.1038/nmat1156
Abstract: There are numerous potential applications for superconducting tapes, based on YBa2Cu3O7-x (YBCO) films coated onto metallic substrates. A long established goal of more than 15 years has been to understand the magnetic flux pinning mechanisms which allow films to maintain high current densities out to high magnetic fields. In fact, films carry 1-2 orders of magnitude higher current densities than any other form of the material. For this reason, the idea of further improving pinning has received little attention. Now that commercialisation of conductors is much closer, for both better performance and lower fabrication costs, an important goal is to achieve enhanced pinning in a practical way. In this work, we demonstrate a simple and industrially scaleable route which yields a 1.5 to 5-fold improvement in the in-field current densities of already-high-quality conductors.
Cross-over between channeling and pinning at twin boundaries in YBa2Cu3O7 thin films
A. Palau,J. H. Durrell,J. L. MacManus-Driscoll,S. Harrington,T. Puig,F. Sandiumenge,X. Obradors,M. G. Blamire
Physics , 2006, DOI: 10.1103/PhysRevLett.97.257002
Abstract: The critical current (Jc) of highly twinned YBa2Cu3O7 films has been measured as a function of temperature, magnetic field and angle. For much of the parameter space we observe a strong suppression of Jc for fields in the twin boundary (TB) directions; this is quantitatively modeled as flux-cutting-mediated vortex channeling. For certain temperatures and fields a cross-over occurs to a regime in which channeling is blocked and the TBs act as planar pinning centers so that TB pinning enhances the overall Jc. In this regime, intrinsic pinning along the TBs is comparable to that between the twins.
Angular dependent vortex pinning mechanisms in YBCO coated conductors and thin films
L. Civale,B. Maiorov,A. Serquis,J. O. Willis,J. Y. Coulter,H. Wang,Q. X. Jia,P. N. Arendt,J. L. MacManus-Driscoll,M. P. Maley,S. R. Foltyn
Physics , 2003, DOI: 10.1063/1.1655707
Abstract: We present a comparative study of the angular dependent critical current density in YBa2Cu3O7 films deposited on IBAD MgO and on single crystal MgO and SrTiO3 substrates. We identify three angular regimes where pinning is dominated by different types of correlated and uncorrelated defects. We show that those regimes are present in all cases, indicating that the pinning mechanisms are the same, but their extension and characteristics are sample dependent, reflecting the quantitative differences in texture and defect density. In particular, the more defective nature of the films on IBAD turns into an advantage as it results in stronger vortex pinning, demonstrating that the critical current density of the films on single crystals is not an upper limit for the performance of the IBAD coated conductors.
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