MAGNETO-OPTICAL OBSERVATIONS OF FLUX DYNAMICS IN ND-BA-CU-O BULK SUPERCONDUCTORS

The magnetic flux dynamics of Nd-Ba-Cu-O (NdBCO) bulk superconductors produced by the Oxygen-Controlled-Melt-Growth (OCMG) method has been i nvestigated using the Magneto-Optical (M-O) technique at various low t emperatures for an external magnetic field applied both parallel (H//c ) and perpendicular (H perpendicular to c) to the c-axis of the sample , While for H//c the flux motion was isotropic, for H perpendicular to c anisotropic penetration and expulsion of the flux lines was observe d directly. In the configuration H perpendicular to c the flux lines w ere observed to move in and out the sample predominantly parallel to t he a-b planes. The flux behaviour has also been correlated to the micr ostructure. Particularly, microcracks along the basal plane were found to provide a low resistance channel for flux motion. (C) 1998 Elsevie r Science S.A. All rights reserved.