Magnetic properties of Bi2212 single crystals with Bi:Sr:Ca:Cu = 2:2:1:2

Bi2212 single crystals having various cation compositions were grown by the floating zone method and evaluated their magnetic properties and resistivity after control of oxygen content by post-annealing. The in-plane anisotropy in the normal state resistivity of Bi2212 single crystals systematically increased with approaching cation compositions to be stoichiometric, 2:2:1:2. This means that disorders in modulation structure due to cation nonstoichiometry strongly affects the in-plane electronic anisotropy of Bi2212. On the magnetic phase diagram under H// c, large differences were not found in the second peak behavior and first order transition (FOT) line of the vortex system between the cation stoichiometric and nonstoichiometric single crystals, while strong bulk pinning was effective up to the FOT line for the former crystals with their irreversibility lines just on the FOT line. In addition, the entropy change of the vortex at the FOT of cation stoichiometric crystals was apparently larger than that of conventional ones. These suggest that more homogeneous and strong superconductivity occurs in the cation stoichiometric “Bi2212” crystals.