Low-field dc magnetization investigations in a Bi2Sr2CaCu2O8 single crystal: observation of a magnetic phase transition at the vortex melting line
Département de Physique de la Matière Condensée, Université
de Genève, 24 quai Ernest-Ansermet, CH-1211 Genève 4, Switzerland
Accepted: 26 January 1996
The mixed-state magnetization of a Bi-2212 single crystal has been investigated with high resolution using a SQUID magnetometer. In the high-temperature region K), we found that the slope vs. H shows a positive step at with Oe and n=1.28. This observation is compatible with a first-order phase transition with a distribution of internal fields, and is attributed to the melting of the 3D vortex lattice. The estimated entropy jump is 1 kB/vortex/layer CuO. However, when T is lower than 50 K, we observe radical changes in M(H); the 3D melting line divides into a decoupling line at a temperature-independent field and the onset of the irreversibility.
PACS: 74.60.Ec – Mixed state, critical fields, and surface sheath
© EDP Sciences, 1996