Analysis of thermo-magnetic fluctuations in Bi1.6Pb0.5Sr2-xLuxCa1.1Cu2.1O8+δ (0.000 ≤ x ≤ 0.125) superconductor

The effect of substitution of rare-earth Lu on the glass transition temperature (T-g), the temperature and magnetic field dependent activation energy [U-0(B,T)] and flux pinning properties of Bi1.6Pb0.5Sr2-xLuxCa1.1Cu2.1O8+delta superconductor was studied. A large broadening of resistive transition in magnetic field is observed which is a direct evidence for the thermal fluctuation in the vortex system and hence the modified vortex-glass to liquid transition theory is used to calculate the values of T-g and U-0(B,T). The resistivity shows a glassy behavior even at higher temperatures and magnetic fields for the Lu stoichiometry x=0.100 which is believed to come mainly from the point defects arised due to the substitution of Lu atoms in the (Bi, Pb)-2212 system. The results also show that the values of T-g, magnetic field dependent activation energy U-0(B) and U-0(B,T) are maximum for x=0.100, which shows that the flux lines are effectively pinned and the vortices are in glassy state for this sample. The enhancement in U-0(B,T) and the flux pinning properties of the (Bi, Pb)-2212 system due to Lu doping has both scientific and technological importance. Also, for temperatures below the superconducting transition temperature (T-C), a scaling of all measured resistivity curves in magnetic field (B=0.4 and 0.8 T) is obtained for each stoichiometry. This scaling obtained in the presence of magnetic field is quite useful for better understanding of the behavior of the vortex-liquid in high temperature superconductors. (C) 2009 Elsevier B.V. All rights reserved.