Magnetic and magneto-transport properties of NdBaCuO single crystals with varying Nd/Ba substitution and oxygen content

The effects of Nd/Ba substitution and oxygen contents on the peak effect of J(c) and transport properties in the normal states of Nd1+yBa2-yCu3O7-x si ngle crystals are studied. We find that the Nd/Ba substitution plays a more important role for the peak effect than the oxygen vacancies in nearly opt imum-doped crystals. In heavily underdoped crystals with y similar to 0, we observe a peculiar charge localization in the out-of-plane and in-plane co nductivity followed by superconducting transition at low temperature. Magne tization studies reveal that this behavior can be explained by the existenc e of spin-glass-like antiferromagnetic ordering above T-c in the oxygen def icient region of x = 0.4-0.6. (C) 2001 Elsevier Science B.V. All rights res erved.