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 (Tg), the temperature and magnetic field dependent activation energy [U0(B,T)] and flux pinning properties of Bi1.6Pb0.5Sr2−xLuxCa1.1Cu2.1O8+δ 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 Tg and U0(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 Tg, magnetic field dependent activation energy U0(B) and U0(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 U0(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 (TC), 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.