Influence of discontinuous columnar defects on flux pinning properties in GdBCO coated conductors

To investigate the effect of discontinuity of 1-D pinning centers on the flux pinning in a wide range of magnetic field directions, discontinuous columnar defects (CDs) and continuous CDs were formed in GdBCO coated conductors using Xe-ion irradiations with 80 and 270 MeV, respectively. An overall shift upward in J_c, for the 80-MeV-irradiated sample compared to the 270-MeV-irradiated one, can be observed in every direction of magnetic field, which is more remarkable as temperature decreases. This implies a synergetic effect of the pinning interaction between the linearity and the discontinuity for the discontinuous CDs. When the density of CDs is lower, however, the difference in J_c between the discontinuous and the continuous CDs becomes less at lower temperature, even in the magnetic field parallel to the c-axis. At lower density of CDs, the average spacing between CDs is wider, which would hardly lead to automatic entanglement of flux lines in the discontinuous CDs, i.e., to the synergetic effect.