Magnetic penetration depth and reversible magnetization in single crystalsof Bi2Sr2CaCu2O8+delta grown by TSFZ method

We analyze the reversible magnetization in Bi2Sr2CaCu2O8+delta using severa l theoretical concepts, starting from the London model. The field dependenc e of the empirical "superfluid density" dM/d In B is fitted with using the theory of circular cell. Additionally, we take into account the pinning mec hanism associated with dislocation structures naturally existing in the cry stals grown by travelling-solvent-floating-zone (TSFZ) technique. This allo ws us to explain: (i) the rapid variation of dM/d ln B at small fields. (ii ) the reduction of thermal fluctuation term with respect to the theoretical prediction for decoupled pancakes. In the light of this reduction we deriv e the curves H-cl (T) and lambda (2)(0)/lambda (2)(T) from the reversible m agnetization similar to the ones obtained by direct measurements of H-cl by micro-Hall AC technique, and with microwave surface impedance, respectivel y. (C) 2001 Elsevier Science B.V. All rights reserved.