Critical currents and pinning mechanisms in directionally solidifiedYBa2Cu3

Abstract

The superconducting properties of directionally solidified YBa 2 Cu 3 O 7 -Y 2 BaCuO 5 composites, with critical currents above 10 5 A/cm 2 at 77 K and zero magnetic field, are reported in a wide variety of samples having very different contents of Y 2 BaCuO 5 ͑211 phase͒ precipitates with different particle size and magnetic fields up to 22 T. The field, temperature, and composition dependence of the critical currents allow us to identify interfacial pinning by 211 precipitates as a very effective pinning mechanism. Nevertheless, single vortex interfacial pinning has a dominant role only in a narrow region below about 1 T and temperatures 40 KрTр80 K. In this region the system shows a behavior very akin to that observed in ion irradiated single crystals and described as correlated disorder. On lowering the temperature the thermal wandering of the vortex from secondary weak pinning centers decreases leading to a new single vortex pinning regime extending up to very high magnetic fields where a mixture of strong and weak pinning centers are active. On the other hand, increasing the magnetic field, the characteristic footprints of the small bundle and large bundle regimes are identified at intermediate temperatures. The former is found below the H-T line given by the maximum of the macroscopic pinning force while the latter is observed above this line up to the irreversibility line. Finally, collecting all these results together a magnetic phase diagram of the mixed state of the YBa 2 Cu 3 O 7 -Y 2 BaCuO 5 textured composites is proposed.

Inhomogeneity of the intrinsic magnetic field in superconducting YBa2Cu3OXcompounds as revealed by a rare-earth EPR probe

“…As it was shown in [25], equation (6) Davidov et al [7] emphasize that in ceramic superconductors a variety of possible mechanisms for flux distribution exists.…”

“…Usually, the value of J C in perpendicular orientation ten times smaller than in a parallel one [25,26]. Therefore, the magnitude of R H Δ for H⊥C could not exceed 9 G even in the high-doped samples at T = 5 K. Taking into account a large linewidth (more than 100 G) and a measurement error (≈ 5 G), the hysteresis might be not detected.…”

“…Nevertheless, we can make a reasonable evaluation. Literature values of J C0 are vary in a wide range from sample to sample in a low-field region: from 10 4 -10 5 A/сm 2 for X ≈ 6.5 in crystals up to ≈ 10 7 -10 8 A/сm 2 in films [25,26,27]. Hence (cf.…”

Vortex liquid entanglement in twinnedYBa2Cu3O7Puig1, Galante2, González3 et al. 1999Phys. Rev. BSelf Cite341151View full textAdd to dashboardCite

“…The main microstructural defect of this material is the micrometric Y 2 BaCuO 5 ͑211͒ precipitates, which are randomly distributed within the superconducting matrix and which strongly enhance vortex pinning in the solid state. 18,19 In the liquid state, however, the random distribution of 211 particles within the matrix should promote vortex entanglement. Thus, the study of the transport properties, which reflects the dynamic behavior of the vortex lattice, should enable the determination of the interplay between the quenched random disorder added by 211 particles and the correlated disorder induced by twin boundaries.…”

Critical currents, pinning forces and irreversibility fields in (YxTm1−x)Ba2Cu3O7 single crystals with columnar defects in fields up to 50 T

“…the critical current j c and the irreversibility field H irr , can be improved by the inclusion of normal particles [1,2,3] or MgO nano-rods [4,5] during growth, by chemical substitution [6], twisters [7], by introducing arrays of sub micrometer holes [8,9,10] and by proton [11] and heavy-ion irradiation [12][13][14][15][16][17][18].…”