Flux lattice melting in twinned NdBa2Cu3O7-y single crystals

We report on the observation of a first-order melting transition of the flux line lattice in a twinned NdBa2Cu3O7-y single crystal by transport and magnetization measurements. The position of kink and hysteresis in resistance, and magnetization jump coincides in the B-T plane. The observed melting transition is a strong function of O2 partial pressure during growth. The first-order transition gradually becomes continuous and a peak in critical current density first emerges with oxygen partial pressure ≥0.07% O2 to Ar atmosphere. The melting line shifts to the low-temperature side due to increasing disorders. The results suggest that the twin planes do not suppress the melting transition in a clean crystal. Our results also demonstrate the existence of a first-order melting transition in a twinned RE-123 system containing rare-earth magnetic ions. (orig.)