Analysis of thermo-magnetic fluctuations in Bi 1.6Pb 0.5Sr 2− xLu xCa 1.1Cu 2.1O 8+ δ (0.000 ≤ x ≤ 0.125) superconductor

Abstract

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 Bi 1.6Pb 0.5Sr 2− x Lu x Ca 1.1Cu 2.1O 8+ 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 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.