ac susceptibility inYBa2(Cu1−x<

The influence of the bulk density on the intergranular superconducting properties of YBa2Cu3−xFexOy (0≤x≤0.01) ceramics

“…This behavior agrees with our previous results of T J m versus X and it can be explained as follows. The T J m decreasing with increasing of X is due to the formation of weak links in the granuls [11,12]. And the observed decrease of T J m with increase of sample's density , as assumed in [7,8], may be caused by the reduction of the role of Josephson vortices pinning which is in its turn due to the reduction of the thickness of intergranular layers.…”

Irreversibility line and low-field grain-boundary pinning in electron-doped superconducting thin films

“…As expected, the above pinning values are larger than those seen in bulk granular materials. [5][6][7] Thus, for small applied magnetic fields, the flux pinning is dominated by the so-called electromagnetic pinning scenario characterized by the London pentration depth rather than the coherence length ͑the latter is responsible for the so-called core pinning scenario in high enough magnetic fields͒. Within this scenario, the observed higher pinning ability of SCCO films near T p can be attributed to a perfect match between the average grain size R and the correspondent London penetration depth S ͑T p ͒.…”

“…While in high enough magnetic fields the dissipation is known to be dominated by the flux motion of Abrikosov vortices, 1-4 the low-field dissipation mechanisms ͑especially, in inhomogeneous and granular superconductors͒ are less obvious due to the numerous grain-boundary related effects which are better treated by the Josephson physics. [5][6][7] Here we present a comparative study of low-field ac magnetic susceptibility data on more homogeneous ͑with a grain size of the order of 2 m͒ Pr 1.85 Ce 0.15 CuO 4 ͑PCCO͒ and less homogeneous ͑with a grain size of the order of 500 nm͒ Sm 1.85 Ce 0.15 CuO 4 ͑SCCO͒ thin films. The main idea of the experiments reported here is to study the influence of inhomogeneity on the dissipative properties of electron-doped thin films via the behavior of the irreversibility line ͑IL͒, T irr ϵ T p ͑H͒, defined as the intergrain-loss peak temperature in the imaginary part of the susceptibility Љ ͑T , H͒.…”

Effect of doping on the superconductive properties of GdBa2Cu3O7−δ single-domain superconductors fabricated in air

“…It might be attributed to the excessive doping of Ga cation and substitutions of Gd-Ba that make the inter magnetic field induced pinning centers spacing less than or equal to twofold and migration of the magnetic flux line easier. Moreover, there are some possible explanations for the negative effect of the excessive doping of ionic Ga on the pinning of magnetic flux: the creation of a weak-link structure inside grains [13]; the increase of the coherence-length anisotropy ratio ( ) which leads to a smaller tilt modulus of the flux lattice and tends to reduce the overall pinning strengths [14]; the decrease of the ability of the Cu-O chains to couple the Cu-O planes [15]; the decrease of the average free energy per unit length of a vortex (␦G/L) which seem to be correlated with the J c values at 77.3 K in the giant flux creep regime [16]. Fig.…”