A COMPARISON OF THE IRREVERSIBILITY LINE BETWEEN MELT-PROCESSED ND-BA-CU-O AND Y-BA-CU-O SUPERCONDUCTORS

In the present work, we have performed a detailed comparative study of the irreversibility line (IL) among flux-grown NdBa2Cu3O7-d (Nd123) s ingle crystal, melt-grown Nd-Ba-Cu-O (NdBCO) and melt-grown Y-Ba-Cu-O (YBCO) bulks by d.c. magnetometry and a.c. susceptometry. ILs were det ermined by measuring d.c. magnetization hysteresis loops, the fundamen tal chi 1 and third harmonic chi 3 signals of a.c. susceptibility for the fields parallel to the c-axis of samples (H//c]. Among these, melt processed NdBCO exhibited the highest IL. On reduced temperature scal e, however, ILs from the chi 3 signals for melt-grown NdBCO and YBCO t ended to merge together, suggesting that real depinning lines are inse nsitive to the field-induced flux pinning centers existing in NdBCO, i ncluding the flux-grown sample, but are rather sensitive to the second ary phase inclusions existing in melt-grown samples. (C) 1998 Elsevier Science Ltd. All rights reserved.