Improved flux pinning and anomalous magnetization peak in heavily overdoped Bi2-xPbxSr2CaCu2-yCryO8+delta single crystals

Flux pinning and anomalous magnetization peak of heavily overdoped Bi2-xPbx Sr2CaCu2-yCryO8+delta [Cr-doping (Bi, Pb)-2212] single crystals are investi gated by means of magnetization measurements with the magnetic field parall el to the c axis. Compared with undoped Bi2Sr2CaCu2O8+delta (Bi-2212) and P b-doping Bi2-xPbxSr2CaCu2O8+delta [(Bi, Pb)-2212] single crystals, the irre versibility line of Cr-doping (Bi, Pb)-2212 single crystals is pronouncedly shifted to high temperatures. The anomalous magnetization peak H-2p with m aximum peak field near 8000 G is observed. The H-2p exhibits strong tempera ture dependence from 0.19 to 0.93T(c). The temperature dependence of H-2p c an be explained according to vortex decoupling theory. The improved flux pi nning may originate from reduced anisotropy due to Pb doping and a sufficie nt number of effective pinning centers due to the random Cr substitution on the Cu site. (C) 2000 American Institute of Physics. [S0003-6951(00)04625- 8].