ANISOTROPIC IRREVERSIBILITY LINES FOR C-AXIS ALIGNED (BI, PB)2CA2SR2CU3O10+DELTA POWDERS

Abstract

Anisotropic irreversibility lines due to thermal fluctuation for quasi-two-dimensional high-T(c) superconductors were observed in c-axis-aligned powders of the (Bi, Pb)2Ca2Sr2Cu3O10+deltaBi(2223) compound with T(c) = 108 K. The anisotropic ratio H(r)(perpendicular-to c)/H(r)(parallel-to c) decreases sharply from 13.6 at 100 K to low values of 3.2 at 80 K and 3.1 at 70 K. The simple 3D-like power law H(r)=a.(1 - T/T(c))n was observed only in the low field region (less-than-or-equal-to 200 G) with n=2.19 for H perpendicular-to c and 2.99 for H parallel-to c. In the higher field region up to 4 kG, the temperature dependence of H(r)(T) lines changes into a 2D-like exponential function H(r) = b.exp (-T/T0) due to the breakdown of the interlayer and/or intralayer coupling of the conduction channel which consists of three Cu-0 planes, with T0 = 14.2 K for H perpendicular-to c and 13.7 K for H parallel-to c. The magnetic susceptibility ratio chi(c)/chi(ab) for this highly anisotropic superconductor in a low applied field of 8 G increases sharply from 9.8 at 5 K to 17.9 near T(c).