Paramagnetic ac susceptibility at the first-order vortex-lattice phase transition

A sharp paramagnetic peak in the local ac susceptibility chi' at the first-order vortex-lattice phase transition in Bi2Sr2CaCu2O8 crystals is found. Observation of this peak establishes the thermodynamic nature of the transition and allows accurate evaluation of the equilibrium magnetization step height, The associated estimated entropy change Delta s reaches values in excess of 6k(B) per pancake vortex close to T-c. The local chi '' shows two independent dissipation peaks. The broader one is caused by the onset of irreversible magnetization, whereas the narrow one is due to hysteresis at the phase transition.