Magnetocaloric effect and main parameters of Bi2Sr2Ca2Cu3Oy textured ceramic superconductor

Low-temperature adiabatic calorimetry in fields up to 4 T is used to study the change in entropy, ΔS, at the transition to the mixed state in Bi2Sr2Ca2Cu3Oy textured ceramics. The slope of the upper critical field was evaluated using magnetoresistance measurements and taking into account a fluctuation contribution to the conductivity at T>Tc. Near Tc ΔS/ΔH≅0.5 Oe K-1 in the direction normal to the ab-plane, dHc2perpendiculartoab/dT≅-0.4 T K-1, dHc2parallelab/dT≅-13 TK-1. These values give the Ginzburg-Landau parameters Kperpendicularto≅16 and Kparallel≅450. It is shown that the region T>60 is a validity interval of the Ginzburg-Landau theory. The value of the lower critical field Hc1(0)≅1300 Oe is estimated. (orig.)