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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1478-1485 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nucleation of domains of inverse polarity is observed in the remanent state of high Tc superconductors using the high-resolution Faraday effect (HRF). The remanent state consists of domains with trapped flux and of domains with opposite polarity, separated from each other by an annihilation zone. It is shown that the stray fields of microstructural defects contribute to the nucleation process. Using the capability of the HRF technique to observe dynamic processes, experimental evidence for the different signs of the vortices is given. The influence of the pinning forces on this behavior is also shown.
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2351-2353 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The flux pinning characteristics of ternary melt-processed (Nd0.33Eu0.33Gd0.33)Ba2Cu3Oy (NEG) superconductors are studied in the temperature range 60≤T≤90 K. NEG samples exhibit a strongly developed peak effect in the dependence of the critical current densities on the external field, Ha. The scaling of the pinning forces versus the reduced field h=Ha/Hirr (where Hirr denotes the irreversibility field) yields a peak at h0=0.5 which is an indication of pinning provided by a spatial variation of the transition temperature. The presence of a weaker superconducting second phase is demonstrated by means of field cooling and warming experiments in fields up to 7 T. Furthermore, we discuss the possible effect of the magnetic moments of Gd and Nd on the flux pinning. © 1998 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3307-3311 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Flux distributions observed on melt-processed YBa2Cu3O7−δ samples are presented with the external magnetic field oriented parallel and perpendicular to the c axis using the high-resolution Faraday effect technique. In this way, flux penetration along and across the Cu–O planes is observed directly. The measured flux density profiles allow a determination of the different critical current densities and show the influence of intrinsic pinning.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 3241-3246 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The scaling of the volume pinning forces, Fp=jc×Ba, is performed versus the reduced fields bf=Ba/Bfp (where Ba is the applied field, and Bfp denotes the peak position of Fp,max) and h=Ha/Hirr (where Hirr denotes the irreversibility field) for two different NdBa2Cu3O7−δ superconductors, a single crystal and a melt-processed sample. In both cases, an excellent natural scaling is found to hold. Based on these good scaling results, we extend the scaling analysis towards lower temperatures. There, the scaling parameters are no longer directly accessible within our experimental field range, but can be deduced from the Fp(Ba) curves normalized using fitting values of Bfp and Fp,max so that these overlap with the high temperature curves. It is shown that such a procedure allows to obtain reasonably good estimates of Fp,max and Hirr, which leads in turn to an estimation of the irreversibility line well down to 0 temperature. At low temperatures, deviations from the analytical dependencies appear which are due to interference with the central and intermediate peak in the magnetization loops. The shape of the irreversibility line is discussed. © 1999 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5705-5711 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The flux pinning behavior of ternary melt-processed (Nd–Eu–Gd)Ba2Cu3Oy superconductors is studied with varying Gd2BaCuO5 second-phase (Gd-211) defect concentrations using magnetotransport and magnetization measurements. The critical current density, Jc increases with the addition of Gd-211 particles displaying a maximum value of Jc for 30% at zero and in intermediate field range and decreases on further addition of Gd-211 particles. A pronounced field-induced bump feature in the resistivity was observed. The dynamic scaling of the resistance suggests the low temperature phase as the vortex-glass phase. The current–voltage characteristics over the whole transition temperature regime show a linear flux–flow type behavior that favors the phenomenon of vortex entanglement in the liquid phase. The Nd/Ba substitution sites along with Gd-211 second-phase particles refined by the addition of a small amount of Pt are one of the possible reasons for the vortex entanglement in the liquid phase. The in-plane and out-of-plane resistance measurements clearly show the correlation of the vortices in the liquid state favoring some influence of twin planes and occasionally occurring natural grain boundaries on the liquid state as well. These defects give rise to high critical current density at low temperature with significant enhancement in pinning favoring the glassy phase to occur. © 1999 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 91-93 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: (Nd0.33Eu0.33Gd0.33)2BaCuO5 (NEG-211) particles are added to ternary (Nd0.33Eu0.33Gd0.33)Ba2Cu3Oy (NEG) bulk, melt-processed superconductors. By means of transmission electron and polarized light microscopy, we found that two types of 211 particles are formed; large NEG-211 and submicron-sized particles containing mostly Gd in the rare earth site are formed which can act as effective flux pinning sites. The critical current density at zero field increases monotonously as a function of the NEG-211 concentration, but the secondary peak vanishes above 40 mol % 211 addition. As a result, a critical current density of 68 000 A cm−2 at 77 K and 2.5 T applied field is achieved with at 40 mol % 211 additions. © 2000 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 253-255 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The flux pinning behavior of ternary melt-processed (Nd–Eu–Gd)Ba2Cu3Oy superconductors is studied with varying defect concentrations using magnetotransport and magnetization measurements. A huge field-induced bump feature in the resistivity with increasing defect density, field-induced magnetization kink and linear voltage-current (V-I) characteristics over the whole transition temperature regime favor the phenomenon of vortex entanglement in the liquid phase. The Nd/Ba substitution sites along with the fine second-phase particles are one of the possible reasons for the vortex entanglement and these defects give rise to high critical current density and reduced dissipation at low temperature with significant enhancement in pinning. © 1999 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 514-516 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An anomalous position of the central peak of magnetic hysteresis loops is observed in (Bi,Pb)-2223/Ag tapes at positive external fields Bext for dBext/dt〈0. We model the grain structure by a system of superconducting disk-shaped grains touching each other in small, but highly conducting contacts at the disk circumferences. The sign of the internal field Bi at the circumference of large, thin well oriented grains in the tape plays an important role. While in great majority of the sample volume Bi is delayed behind Bext, just at the grain circumferences Bi might be considerably ahead of Bext. Based on these considerations, a model sample which should exhibit similar features of the central peak is proposed.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6798-6800 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Flux patterns of multifilamentary Ag-sheathed (Pb,Bi)2Sr2Ca2Cu3O10+δ tapes comprising 19 filaments are visualized by means of magneto-optic imaging. In low fields, the shielding currents are seen to flow mainly in the outermost filaments. With increasing external magnetic field, the inner filaments also contribute to the current flow. To compare the local flux distribution with the integral magnetization values, magnetization loops are measured by a SQUID magnetometer on the same sample following the fields used in the magneto-optic imaging (± 120 mT) and covering fields up to ±5 T at various temperatures. The magnetization loops also reveal that the multifilamentary tapes show the anomalous position of the central peak, but always less pronounced than in monofilamentary tapes. © 1998 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 768-770 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using the high-resolution Faraday effect, the flux penetration into YBa2Cu3Ox thin films grown over one or two substrate step edges is directly observed at a temperature of T=5 K. The regions at the steps are easily penetrated by the flux already present at low applied external magnetic fields due to the locally enhanced stray fields. The step edges are found to separate the sample magnetically into independent parts. It is also shown that the local observation of flux penetration allows detection of the influence of defects in the thin-film samples on the domain structures in a direct way.
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