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Search Results: 1 - 10 of 650236 matches for " H. Wang J. L. Macmanus-Driscoll "
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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.
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.
Induced magnetization in La$_{0.7}$Sr$_{0.3}$MnO$_3$/BiFeO$_3$ superlattices
S. Singh,J. T. Haraldsen,J. Xiong,E. M. Choi,P. Lu,D. Yi,X. -D. Wen,J. Liu,H. Wang,Z. Bi,P. Yu,M. R. Fitzsimmons,J. L. MacManus-Driscoll,R. Ramesh,A. V. Balatsky,Jian-Xin Zhu,Q. X. Jia
Physics , 2014, DOI: 10.1103/PhysRevLett.113.047204
Abstract: Using polarized neutron reflectometry (PNR), we observe an induced magnetization of 75$\pm$ 25 kA/m at 10 K in a La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO)/BiFeO$_3$ superlattice extending from the interface through several atomic layers of the BiFeO$_3$ (BFO). The induced magnetization in BFO is explained by density functional theory, where the size of bandgap of BFO plays an important role. Considering a classical exchange field between the LSMO and BFO layers, we further show that magnetization is expected to extend throughout the BFO, which provides a theoretical explanation for the results of the neutron scattering experiment.
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.
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.
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.
Temperature dependence of the microwave surface impedance measured on different kinds of MgB$_2$ samples
A. A. Zhukov,L. F. Cohen,A. Purnell,Y. Bugoslavsky,A. Berenov,J. L. MacManus-Driscoll,H. Y Zhai,Hans M. Christen,Mariappan P. Paranthaman,Douglas H. Lowndes,M. A. Jo,M. C. Blamire,Ling Hao,J. Gallop
Physics , 2001,
Abstract: In this paper we present the results of measurements of the microwave surface impedance of a powder sample and two films of MgB$_2$. One film has $T_c=30$ K and is not textured, the other is partially c-axis orientated with $T_c=38$ K. These samples show different types of temperature dependence of the field penetration depth: linear for the powder sample, exponential with $\Delta/kT_c<1.76$ (film with $T_c=30$ K) and strong coupling behaviour with $\Delta/kT_c\sim 2.25$ (film with $T_c=38$ K). The results are well described in terms of an anisotropic gap model or presence of a slightly deficient MgB$_2$ phase. The data set for all samples - taken as a whole cannot be fitted into a two gap scenario.
The structure of the superconducting gap in MgB2 from point-contact spectroscopy
Y. Bugoslavsky,Y. Miyoshi,G. K. Perkins,A. V. Berenov,Z. Lockman,J. L. MacManus-Driscoll,L. F. Cohen,A. D. Caplin,H. Y. Zhai,M. P. Paranthaman,H. M. Christen,M. Blamire
Physics , 2001, DOI: 10.1088/0953-2048/15/4/308
Abstract: We have studied the structure of the superconducting gap in MgB2 thin films by means of point-contact spectroscopy using a gold tip. The films were produced by depositing pure boron on a sapphire substrate, using e-beam evaporation, followed by reaction with magnesium vapour. The films have a Tc of 38.6 +- 0.3 K and resistivity of about 20 microOhm cm at 40 K. The point-contact spectra prove directly the existence of a multi-valued order parameter in MgB2, with two distinct values of the gap, DELTA1=2.3+-0.3 meV and DELTA2=6.2+-0.7 meV at 4.2 K. Analysis of the spectra in terms of the Blonder-Tinkham-Klapwijk model reveals that both gaps close simultaneously at the Tc of the film. Possible mechanisms that can explain the intrinsic co-existence of two values of the gap are discussed.
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