OBSERVATION OF MULTIPLE PEAKS IN THE MAGNETIZATION CURVES OF NDBA2CU3O7 SINGLE-CRYSTALS

Induced current densities j(s)(T,B) were measured in a wide temperatur e (5 less than or equal to T less than or equal to 90 K) and field ran ge (0 less than or equal to mu(0)H(a) less than or equal to 7 T) on si ngle crystals of NdBa2Cu3O7-delta using a superconducting quantum inte rference device magnetometer. The samples exhibit the fishtail or peak effect at temperatures above 30 K. In a small temperature window betw een 50 and 74 K, three peaks are seen in the j(s)(T,mu(0)H(a)) curves. The temperature and field behavior of the induced current densities i s analyzed using a model describing a magnetization curve as composed of two independent contributions at low and high fields. By means of t his analysis, it is demonstrated that the third peak corresponds to th e fishtail peak, whereas the position of the second peak is practicall y independent of temperature. It is shown that the appearance of the s econd peak is due to the large values of the position of the fishtail peak.