Magneto-Optical Studies of Chemical Inhomogeneities in Bi2212 Single Crystals

Abstract

A detailed characterization of chemical inhomogeneities in Bi2212 single crystals was carried out by combining compositional analyses using wave dispersive spectroscopy (WDS) and local magnetization measurements, such as magneto-optical imaging (MOI) technique and Bitter decoration technique. According to the chemical analyses using WDS, there are two types of inhomogeneities; one with linear structures extending toward a-axis, and another with sheet like structures that lying along a-axis. The line defects relate with the compositional inhomogeneities, such as Ca-enriched or Ca-deficient regions, with width ranging from a few nanometers to micrometers and lie parallel to the crystal a-axis. It was found that the flux line arrangement at the defect region is largely affected by the type of nonstoichiometry.The flux line lattice (FLL) with a hexagonal order was observed in the Ca-enriched region, while no FLL in the Ca-deficient region. On the other hand, the crystal with sheet-like inhomogeneities showed a “zebra-like” flux penetration and trapping behavior, suggesting that it composes of two regions with different pinning properties. WDS analyses revealed that Ca content is also different between these two regions.