Decoration of flux pinning positions in YBa2Cu3O7−δ superconductors

Flux pinning in the sintered high Tc oxide superconductors, YBa2Cu3O7−δ, in the vortex state has been demonstrated for the first time using the Bitter pattern technique and scanning electron microscopy. External magnetic fields of 150 or 800 G perpendicular to the specimen surfaces were applied during the evaporation of cobalt after the specimens cooled with liquid nitrogen had reached a temperature below Tc. All specimens thus decorated with cobalt show nonuniformly distributed flux pinning positions as would be expected due to the porosity and multiphase character of the specimens as well as the relatively low field applied.