Microstructures and critical current densities of YBCO films containing structure-controlledBaZrO3 nanorods

Abstract

BaZrO3 nanorods are known to be effective pinning centers asc-axis-correlated pinning centers. Furthermore,BaZrO3 nanorodsin REBa2Cu3Oy (RE: rare-earth element) films are formed by self-assembled stacking ofBaZrO3 using a target mixture of a superconductor andBaZrO3 for pulsed-laser deposition, which is a very easy fabrication technique. The density ofBaZrO3 nanorodsin YBa2Cu3Oy (YBCO) films can be controlled by varying theBaZrO3 content in atarget. The BaZrO3 addition has two functions for superconductivity; one is the improvementof pinning forces due to the addition of pinning centers and the other isTc degradation.The optimum BaZrO3 addition for Jc improvement in magnetic fields is found to be around 3 wt% because of atrade-off between the two functions described above. Furthermore, the length ofBaZrO3 nanorods is found to be controlled using two types of target: pure YBCO and a mixture of YBCO andBaZrO3. Varyingthe BaZrO3 nanorod length has an effect on the pinning mechanism. In particular, magnetic field angle dependences ofJc are variedfrom c-axis-correlated pinning to nearly random pinning by changing the nanorod length. Themagnetic field at the crossover of the pinning mechanism seems to be adjusted by theBaZrO3 nanorod length.