Speaker
Description
An introduction of artificial pinning centers (APC) is one of the key techniques to improve a large anisotropy in critical current density $J_c$ REBa$_2$Cu$_3$O$_y$ (RE123, RE: Y and rare earth) tapes. The APC technique is utilized in the practical RE123 coated conductors, recently. One of the most promising APCs is a BaMO$_3$ (M; Zr, Sn, Hf, etc) nanorod, which is a nano-scaled columnar-shaped precipitate. However, the effect of nanorod strongly depends on its size and alignment. In the case of the well-aligned nanorod, which is an ideal case as a c-axis correlated pinning center, the matching field limits the $F_p$ behavior and thus the $F_p/F_p^{max}$ curves are scaled against magnetic field below the matching field but are enhanced in high fields above the matching field with decreasing temperature. This can be explained by the cooperation of the random and correlated pinning model. On the other hand, in the case of the inclined nanorod, the scaling behavior of $F_p-B$ curves below the matching field disappears, and the random pinning contribution appears depending on the nanorod’s alignment. On the other hand, the conventional $F_p$ scaling behavior in $F_p/F_p^{max}$ vs $B/B_{max}$ is observed in the Sm123 tapes without APCs. If we compared the angular dependence of $J_c$ between Sm123 tapes with and without APCs, the enhancement of $J_c$ due to the APC for $B$//c can be seen even at 4.2 K and high fields up to 25 T although the no c-axis peak in angular dependence of $J_c$. Based on the angular and field dependences of $J_c$ in wide temperatures and high magnetic fields up to 27 T, we discuss the correlated and random pinning effects in the Sm123 tapes with and without nanorods.
Acknowledgments: A part of this work was supported by JST-ALCA.
