We investigated the magnetic flux dynamics of Nd-Ba-Cu-O (NdBCO) bulk superconductors produced by the Oxygen-Controlled-Melt-Growth (OCMG) method using the Magneto-Optical (M-O) technique at various low temperatures. An external magnetic field was 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 were directly visualized. 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 behavior was also correlated to the microstructure. Particularly, the microcracks along the basal plane were found to provide a channel for easy flux motion. The anisotropic behavior of the flux front reflects the anisotropy in the critical current density Jc. The different components of Jc were independently calculated from the M-O data directly analyzing the magnetic induction profiles. These Jc values were consistent with those estimated interpreting the magnetization hysteresis measurements within the framework of the extended Bean model.
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