Superconductor pinning

Type B gelatin, 12 440-441 Type II anion exchangers, 14 390 Type I/II zwitterionic SCK micelles, 20 490 Type II metallic superconductors, pinning force in, 23 826... 

High performance sealants, 22 28 High phosphorus alloys, corrosion performance of, 9 710-711 High pinning Type II superconductors, 23 High pressure apparatus, 13 413 High pressure applications, 13 436-448 in commercial products, 13 436-438 in inorganic chemistry reactions, 13 440—448... 

The symmetry changes of the vortex lattice in borocarbide superconductors affect their pinning properties as was shown for YNi2B2C (Silhanek et al. 2001). For the field orientation // c, the reorientation transition of the vortex lattice mentioned above was found to be associated with a significant kink in the volume pinning force Fp, whereas in the basal plane (for H c) the signature of nonlocal effects is a fourfold periodicity of Fp. 

Defects in crystals are known to have a potentially major influence on phase behavior. For instance, dislocation unbinding is believed to be central to the 2D melting transition, while in 3D there is evidence to suggest that defects can act as nucleation centers for the liquid phase [105]. In superconductors, defects can pin vortices and influence vortex melting [106]. 

The stable flux pattern in Figure 55(a) forms due to the penetration of a magnetic flux front of pinned vortices from the sample surface. The joule heating arising from vortex motion can release global flux jumps and thermal quench instabilities under certain conditions which have to be avoided for stable operation of current-carrying superconductors (Mints and Rakhmanov, 1981). Dendritic flux patterns which have been observed in Nb disks (Goodman and Wertheimer,... 

Frozen current vortices (FCV) in superconductors can serve as essential elements of magnetic recording and as a convenient subject for investigations magnetic flux pinning at a transport current / across the superconductor, annihilation of two FCV with opposite magnetic flux, quantum behavior of frozen magnetic flux in the FCV, collective flow of FCV under the influence of the transport current I (Fig.5a). 

Johansen, T.H. (2000) Flux-pinning-induced stress and magnetostriction in bulk superconductors, Supercond. Sci. Technol. 13, R. 121-37. 

In this paper, we concentrate on the /j+SR measurements and determine if YBa2Cu307 is a bulk. v-wave (nodeless) superconductor, as determined in Refs. 1-3, or a d-wave superconductor, whose order parameter A(k), changes sign as a function of k, as claimed in Ref. 8. In making this determination, we show that the features observed in the single-crystal data of Ref. 8 are actually due to temperature-activated fluxon de-pinning, an effect which is not readily observable in strongly pinned systems such as the early powder samples or the early heavily-twinned crystals. 

Further examples of positron study of defects in HTSC are studies carried out to understand the nature of flux-pinning defects that lead to an increase in critical-current density on neutron-irradiated Y 1 2 3. Experiments [59] on positron lifetime and critical-current density measurements on various neutron-irradiated samples of Y 1 2 3 indicate that the critical current density is correlated with the micro-void density, as obtained from the analysis of positron lifetime measurements. Investigation of defects in other HTSC superconductors, such as La-Sr-Ca-Cu-0 [60], Bi-Sr-Ca-Cu-0 [49], and Nd-Ce-Cu-O [52], have also been carried out. 

For strong type-II superconductors a difference may exist between B 2 obtained from ac-susceptibility data and the thermodynamically relevant upper critical field, 5c2, for which (2.13) and (2.14) were derived originally. Prom extensive work on high-Tc cuprates it is known that B 2 is related to the so-called irreversibility line [196]. The basic idea of a semiquantitative flux-creep theory [197] is that pinned vortices can be activated thermally over an energy barrier Uq resulting in a reduced critical current of the form [196]... 

The temperature dependence of B 2 is shown in Fig. 2.29 by open circles [183]. The data reveal a positive curvature which has been observed for many other organic superconductors by ac-susceptibility and resistivity measurements. The solid line is a one-parameter fit using (2.17) for fixed / which describes the data down to the lowest temperature. The exact temperature dependence of B 2 depends on the detailed nature of the pinning centers which... 

Magnetic flux pinning effect of impurities in copper oxide superconductors... 

With the use of the DV-Xa molecular orbital method, electronic structure calculations have been performed to investigate the impurity effect on material properties. Firstly, calculations were done for F atoms substituted for 0 (oxygen) atoms in copper oxide superconductors. It was found that the population of the atomic orbitals of F atoms is small in HOMO (highest occupied molecular orbital) and a small fraction of charge carriers enters the impurity sites. The F impurities are therefore expected to be effective for pinning magnetic flux lines in Cu oxide superconductors. 

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