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 investigated using the Magneto-Optical (M-O) technique at various low temperatures for an external magnetic field applied both parallel (H//c) and perpendicular (H⊥c) to the c-axis of the sample. While for H//c the flux motion was isotropic, for H⊥c anisotropic penetration and expulsion of the flux lines was observed directly. In the configuration H⊥c the flux lines were observed to move in and out the sample predominantly parallel to the a-b planes. The flux behaviour has also been correlated to the microstructure. Particularly, microcracks along the basal plane were found to provide a low resistance channel for flux motion.