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

Abstract
A sharp paramagnetic peak in the local ac susceptibility χ at the first-order vortex-lattice phase transition in Bi2 Sr2CaCu2 O8 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 Δs reaches values in excess of 6kB per pancake vortex close to Tc. The local χ 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.