MAGNETIC PHASE-DIAGRAM OF ANISOTROPIC LAYERED SUPERCONDUCTORS VIA MAGNETIZATION MEASUREMENTS FOR H-VERTICAL-BAR-VERTICAL-BAR-C IN BI2212

The Bi2Sr2CaCu2O8 system is viewed as an archetypal of superconductors modelled as Josephson coupled CuO2 bilayers. The isothermal and tempe rature dependent DC and AC magnetization measurements for H parallel-t o c in a single crystal of Bi2212 have been performed. Qualitative cha nges are observed to occur over a narrow range of temperature values b efore reaching the superconducting-normal transition. The observed beh aviour can be ascribed to the rapid variation in the strength of the c oupling between the superconducting CuO2 planes (i.e., bilayers in the case of Bi2212). Strongly coupled planes behave like a 3D superconduc tor, whereas weakly coupled planes have a two component response attri butable to 2D planes and interplanar couplings. We believe that this p aper is a plethora of new findings. Our observations imply that resist ivity across the planes becomes zero earlier than that within the plan es. A new line (designated as H2D(T)) above which the change in the el ectromagnetic response is dominated by quasi 2D-planes has been determ ined for the first time. This paper also contains the first observatio n of Differential Diamagnetic Effect (DDE) in the In-phase AC suscepti bility data which signals the onset (at T2D(H)) of dominance of respon se from 2D-planes. In addition to a host of interesting thermomagnetic history effects which are a consequence of interplay between the diam agnetic responses from the two components, a comparison of irreversibi lity lines (of the 3D state) determined by different methods on the sa me specimen of a HTSC is also being presented for the first time. We h ave come across Paramagnetic Meissner Effect (PME), first recognized i n ceramic samples of Bi2212, in the temperature region of dimensional crossover in our single crystal sample, which inter-alia confirms our labelling of the two component behaviour. A schematic phase diagram su mmarizing the various transformations that can occur near T(c) in the electromagnetic response of an anisotropic layered system has been dra wn.