EFFECT OF Y2BACUOX PRECIPITATES ON FLUX PINNING IN MELT-PROCESSED YBA2CU3OX

Magnetic hysteresis data have been taken at 4.2, 50, and 77 K over a wide range of magnetic field on three types of melt-textured YBa2Cu3Ox (123) samples: stoichiometric 123, 123 + 6 mol% Y2BaCuO5 (211) particles, and quench-melt-growth-processed (QMGP) 123 + 6 mol% 211. In order to obtain accurate comparisons of the intragranular critical current densities, the magnetization measurements were performed on finely powdered samples, the average particle size of which was less than the grain size of the original sample. The QMGP samples exhibited substantially larger hysteresis at 4.2 and 50 K, indicating significantly enhanced flux pinning at these temperatures. At 77 K, however, although the hysteresis loop of the QMGP samples was largest at low fields, the hysteresis difference, DELTA-M, decreased more rapidly with field than did the DELTA-M of the stoichiometric melt-processed sample. A possible pinning mechanism related to the observed hysteretic behavior is discussed.