ANISOTROPY OF THE IRREVERSIBLE MAGNETIC-BEHAVIOR OF YBACUO AND TLBACACUO SINGLE-CRYSTALS - A COMPARATIVE AC-SUSCEPTIBILITY STUDY

Applying an a.c.-susceptibility technique, the lower critical fields HC1(T) as well as the irreversibility lines Hc*(T/Tc) ~ (1- T/Tc)∞ have been determined for YBaCuO and T12Ba2aCu2O8 single crystals. Pronounced anisotropies are observed for the above quantities in both systems indicating the strong influence of the Cu-0 planes. As a main result, the exponent a describing the temperature behaviour of the irreversibility lines is found to exhibit a clear dependence on the field orientation: if the field is oriented perpendicular to the Cu-0 planes, one observes a=4/3 for both HTSC systems. For fields parallel to the Cu-0 planes a = 312 for YBaCuO and α = 1 for T12Ba2aCu2O8. © 1990 IOP Publishing Ltd.