CHI'' PEAK MEASUREMENTS IN HTSC SINGLE-CRYSTALS

The use of AC inductance techniques to measure AC absorption (chi") in high-temperature superconducting materials is discussed. A single sharp peak in chi" versus temperature is typically seen for good crystals of YBa2Cu3O7-x. However, some crystals of this material show multiple chi" peaks which have different magnetic field and frequency dependences. Crystals of Bi2Sr2Ca1Cu2O8+y and Tl2Ba2Ca1Cu2O8+y show only single chi" peaks. Magnetic field, temperature, and measurement frequency dependences of chi" of these materials are presented. A critical state model is used to interpret these results. Multiple peak behavior is explained as the presence of different superconducting domains in the crystals. Attempts to alter these domains by modifying the oxygen content and distribution in crystals of YBa2Cu3O7-x by oxygen annealing were unsuccessful. Etching experiments did not show any surface contribution to the magnetic properties of these samples.