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) 2 Ca 2 Sr 2 Cu 3 O 10+δ Bi(2223) compound with T c =108 K. The anisotropic ratio H r (⊥c)/H r (//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 (≤200 G) with n=2.19 for H⊥c and 2.99 for H//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/T 0 ) due to the breakdown of the interlayer and/or intralayer coupling of the conduction channel which consists of three Cu-O planes, with T 0 =14.2 K for H⊥c and 13.7 K for H//c. The magnetic susceptibility ratio χ c /χ 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 . © 1992 The Japan Society of Applied Physics.