DOPING LEVEL DEPENDENCE OF MAGNETIZATION ANOMALIES AND HEAT-CAPACITY OF BI2SR2CACU2O8-STATE(DELTA IN THE MIXED)

Magnetization M and heat capacity C were measured around the first ord er vortex phase transition lines of two Bi2Sr2CaCu2O8+delta single cry stals having different oxygen contents. The entropy jump per vortex pe r layer, Delta s, at the transition was estimated from the step in M. The oxygen-content dependence of bs was contradictory to the simple vo rtex lattice melting theory based on the Lindemann criterion. In both crystals, no anomalies in C were observed at the transition owing to b oth the small Delta s and the broadening of the transition.