Vortex pinning phase diagram for various kinds of c-axis correlated disorders in RE123 lms

摘要

The critical current density J_c and resistivity ρ of REBa_2Cu_3O_x (RE123) lms were evaluated in high magnetic eld and wide temperature regions. We use three di erent samples such as a heavy ion irradiated Y123 lm, a BaZrO_3 (BZO) added Y123 lm and a low temperature growth Sm_(1-x)Ba_(2+x)Cu_3O_y (LTG-Sm123) lm. In these lms, there exist the di erent c-axis correlated disorders like columnar shaped ssion tracks for the heavy ion irradiated Y123 lm, columnar shaped BZO precipitates for the BZO added Y123 lm and edge dislocations at grain boundaries for the LTG-Sm123 lms. The large peak of the angular dependence of J_c for B//c direction was observed for all samples measured in this study in a low eld region, suggesting that the c-axis correlated pinning works well for these samples. However, we found that the behavior of the J_c peak for B//c strongly depends on a sort of c-axis correlated pinning centers. In the case of the columnar shaped ssion tracks in the Y123 lm, the J_c peak for B//c increases monotonically with increasing a magnetic eld and seems to be connected with the dip structure in the angular dependence of ρ. In the case of the columnar shaped BZO precipitates, however, the J_c peak for B//c vanishes in a high eld region above a few tesla and no dip behavior of ρ was observed. On the contrary, in the case of the edge dislocations for LTG-Sm123 lm, the J_c peak for B//c shrinks with increasing eld and almost vanishes. But it grows again with further increasing a magnetic eld and the dip of the angular dependence of ρ is also observed. Hence the vortex pinning phase diagram strongly depends on a sort of c-axis correlated pinning centers. It is considered that these di erent behaviors of the J_c peak for B//c are related to the competition of the random and c-axis correlated pinnings.