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Abstract |
Magnetization and susceptibility measurements show a first order phase transition in the magnetic flux structure at the irreversibility line of Bi$2$Sr$2$CaCu$2Ο8$ single crystals, in the field range $0 < H < 360$ Oe. The resistivity in the c direction drops six orders of magnitude in less that 0.1 K, and there is a discontinuous change in the magnetization at the same temperature. The change in magnetization together with the Clausius-Clapeyron equation gives a variation of entropy of 0.06kB per vortex layer, at the transition. Above 360 Oe the previous $H-T$ phase diagram is determined by the laminar nature of superconductivity and the irreversibility line is frequency dependent. |
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