Temperature dependence of the magnetic-flux penetration into disk-shapedYBa2Cu3

Abstract

Temperature dependence of the penetration of magnetic flux into YBa 2 Cu 3 O 7Ϫ␦ disk-shaped thin films was investigated at low magnetic fields. We studied the conditions characteristic of complete and incomplete flux-penetration states. The experimental procedure involved the measurements of the profiles of trapped magnetic flux as a function of temperature and the decays of trapped flux at various points across the disk. We determined temperatures and magnetic fields at which the crossover between incomplete and complete flux penetration occurs. This crossover is governed by the temperature dependence of the critical current density. The distributions of the critical currents across the disk in the complete flux-penetration state were found to be temperature independent. No evidence for the Bean-Livingston surface barriers has been found.

Evolution of self-organized bulk vortex structure induced by hole doping in the high-temperature superconductorYBa2Cu3O7−δ

“…This is a contactless technique which allows one to distinguish between the magnetic field due to the circulating persistent current and that due to the trapped vortices in the ring's bulk. 11 In our experiments, we gradually increased ␦ and reduced the hole-doping p, i.e., the number of holes per Cu atom of the CuO 2 planes, by annealing the film in flowing argon at a temperature of 175°C. This was done a number of times in steps of a few hours each so that T c was reduced from 88 down to 55.5 K. The relatively low annealing temperature ensured the reduction in the hole doping by removing oxygen from YBCO without affecting extended defects, such as dislocations and grain boundaries.…”

Observation of the out-of-plane magnetization in a mesoscopic ferromagnetic structure superjacent to a superconductor

“…2 A multitude of techniques have been utilized for the real space observation of flux penetration in superconductors. [3][4][5][6][7] While techniques such as scanning tunneling microscopy have high spatial resolution, 8 they are limited in the scanning area. Conversely, imaging techniques based on the Faraday effect provide wavelength-limited resolution for large imaging areas.…”