Magnetization measurements of single-crystal Pb2Sr2(Y,Ca)Cu3O8: Determination of the coherence length and upper critical field

Magnetization measurements of single-crystal Pb2Sr2(Y,Ca)Cu3O8 from 5 to 250 K in a field of 1.5 T show that, with the field oriented perpendicular to the c axis of the crystal, there is a sharply defined onset of diamagnetism at Tc while with the field parallel to the c axis, the transition is rounded and the diamagnetism present above Tc as a result of superconducting fluctuations. The three-dimensional critical region just above Tc is found in the latter case to be ≊2 K in width. Via analysis of the two-dimensional regime above this critical region, a value of 11 Å for the zero-temperature ab-plane coherence length, ξab(0), is obtained. Using this value for ξab(0) the temperature-dependent magnetization in the vicinity of Tc for various field strengths is analyzed to extract the temperature dependence of the in-plane upper critical field, Hc2∥ near Tc. In addition, the temperature dependence of both Hc2∥ and Hc2⊥ is determined directly from the linear onset of diamagnetism and the critical-field slope for Hc2∥ is in good agreement with that derived from the fluctuation analysis.