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, DELTA-S, 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 > T(c). Near T(c) DELTA-S/DELTA-H almost-equal-to 0.5 Oe K-1 in the direction normal to the ab-plane, dH(c2)perpendicular-to ab/dT almost-equal-to -0.4 T K-1, dH(c2)parallel-to ab/dT almost-equal-to -13 T K-1. These values give the Ginzburg-Landau parameters kappa perpendicular-to almost-equal-to 16 and kappa parallel-to almost-equal-to 450. It is shown that the region T > 60 K is a validity interval of the Ginzburg-Landau theory. The value of the lower critical field H(c1) (0) almost-equal-to 1300 Oe is estimated.