Magnetotransport properties and the irreversibility line in ceramic DyBa2Cu3O7-delta

We report on magnetoconductivity, magnetization and Hall effect measurement s near the superconducting transition of granular DyBa2Cu3O7-delta samples. The resistive transition proceeds in two stages. Decreasing the temperatur e, we first observe the pairing transition, which stabilizes superconductiv ity within the grains. At a lower temperature occurs the coherence transiti on, where the phases of the order parameter in individual grains become lon g-range ordered and a zero-resistance state sets in. The irreversibility li nes determined from zero field cooling and field cooled cooling magnetoresi stance and magnetization experiments are coincident and show a behavior whi ch is typical of the spin glass systems. The Hall effect is hole-like and s hows a sign reversal in temperatures nearly below T-c. (C) 2001 Published b y Elsevier Science B.V.