Overcoming optimization constraint for J_c by hybrid pinning in YBa₂Cu₃O₇ films containing nanorods

Critical current density (J_c) in YBa₂Cu₃O₇ films are improved by nanorods. J_c increases with increasing the nanorod content up to an optimum content, and decreases after exhibiting a maximum due to degradation of the nanorod structure. To overcome this optimization constraint, hybrid pinning consisting of multiple types of pinning centers was investigated. In the present study, Y₂O₃ nanoparticles were additionally introduced into the YBa₂Cu₃O₇ films containing high density BaHfO₃ nanorods to increase the effective matching field. As a result, the global pinning force maximum was shifted to high magnetic field, and the J_c was improved especially in high magnetic field. Thus, even in the case that the J_c improvement in the YBa₂Cu₃O₇ + BaHfO₃ was difficult by increasing the nanorod content, the Y₂O₃ addition successfully improved the J_c. This demonstrates that the hybrid pinning can overcome the optimization constraint for J_c in the YBa₂Cu₃O₇ films containing nanorods. (author)