IRREVERSIBILITY LINE DETERMINATION IN HIGH Tc SUPERCONDUCTORS

Abstract

The irreversibility line has been determined for three different polycrystalline supercQnducting samples. These samples are of composition (Bh.6 Pbo.3 SbO. I)Sr2 Ca2 CU3 0 9-0 , YI Ba2 CU3 0 7-5 and HgI Ba2 Ca2 CU3 Ox+8. The irreversibility line has been obtained from two methods, viz. vanishing of hysteresis in dc magnetization loops and comparing the temperature dependence ofField Cooled (FC) and Zero Field Cooled (ZFC) ac susceptibilities. Both the methods give very close results. The irreversibility field H* obeys a relation of the form: H* = Reo [I -TITer The value ofn lies in the range 0.6 ~ n ~ 0.8. The form of this irreversibility line is compared to the literature and possible explanation ofn ~ 0.66 is given in terms of the Re2(T) dependence observed for at least one of the sample.