Effect of the chemical inhomogeneity on the vortex lattice observed by the Bitter decoration technique in high-T c superconductors

We have performed local magnetization measurements on Bi2SrCa2Cu2O8+y (Bi2212) single crystals grown by TSFZ method using Bitter decoration technique and MO imaging technique, which provides information of static vortex structures at the surface of superconductors. MO image revealed the presence of micron-scale inhomogeneities of critical currents, which is ascribed to the chemical fluctuation as analyzed by WDS. We could successfully observe nanometer-scale line defects with Bitter decoration technique performed at 65 K. The observed structure was largely disordered, presumably due to thermally activated motion during the decoration