Decorations of magnetic flux pinning positions on the (001) face of a single crystal of high-T c superconductor YBa2(Cu, Au)3O7-δ

The Bitter pattern technique has been used in order to decorate the magnetic structures, exhibited by a single crystal of the high-T c superconductor YBa2(Cu, Au)3O7-δ at 4·2 K as a function of the applied magnetic field in a ‘field-cooling’ condition. The decoration reproducibility of some structural faults, under different magnetic fields, has been examined. The two-dimensional lattice of magnetic flux lines, rectangular at low fields, has been found to evolve towards a hexagonal symmetry at elevated magnetic fields; the variation in the average Wigner—Seitz cell area, relative to a magnetic flux line quantum, appears to be inversely proportional to the applied magnetic fields.