SUPERCONDUCTING DIAMAGNETIC MAGNETIZATION OF SINGLE CRYSTALLINE BI2SR2CACU2O8+DELTA

Diamagnetic moment of single crystalline Bi2Sr2CaCu2O8+delta has been measured in magnetic fields between 1G and 5T and in temperatures between 5K and 300K. It is observed that above T(c) even as high as approximately 200 K temperature dependent diamagnetism for the c-axis gradually grows with approaching T(c), whereas that for the ab-plane is nearly constant. This phenomenon is attributed to the superconducting fluctuation effects. Below T(c), the irreversibility line sharply separates the vortex state in magnetic fields into two regions: reversible and irreversible regions in the B-T phase diagram. It seems that large irreversible and hysteresis magnetization at low temperatures partly originates from pinning effects in usual sense but the fast relaxation of diamagnetic moment cannot be accounted for by the flux-flow effect only. A region between the irreversibility line and B(c2), shows reversible magnetization with strong magnetic field dependent partial derivative M(B, T)/partial derivative T near T(c). This is in strong contrast with the Ginzburg-Landau mean field approach and suggests that superconducting fluctuation effects play an important role in this compound.