Magnetization steps near the irreversibility line in a mercury-based superconducting cuprate

Steps in the equilibrium magnetization curves of a (Hg0.8CU0.2)Ba2CUO4 divided by delta (Hg-1201) single crystal have been detected in bulk magnetic measurements. The associated transition line in the H-T plane can be reasonably accounted for by melting or decoupling models, both leading to nearly the same value of the anisotropy parameter. The entropy changes dong this line have been inferred from the height of the magnetization steps by assuming the underlying transition to be of first order. The order of magnitude of this entropy change, as well as its field and temperature dependences, is discussed in comparison to the available literature on other high-T-c superconductors.