Low-field dc magnetization investigations in a Bi
- B. Revaz
- G. Triscone
- L. Fabrega
- A. Junod
- J. Muller
DOIAbstract
The mixed-state magnetization $M(H\|c,T)$ of a Bi-2212 single crystal has been investigated with high resolution using a SQUID magnetometer. In the high-temperature region $(50\;{\rm K}<T<T_{\rm c}=80.2$ K), we found that the slope $\partial M/\partial H|_T$ vs. H shows a positive step at $H_{{\rm trans}}(T)\approx H_0\times(1-T/T_{\rm c})^n$ with $H_0=2340$ 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-indepe...
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