Flux pinning properties and microstructure of SmBa_2Cu_3O_y thin films with systematically controlled BaZrO_3 nanorods

摘要

We report a way of tuning the flux pinning properties by controlling the size and number density of BaZrO_3 (BZO) nanorods without much degradation of the superconducting properties. The BZO nanorods in REBa_2Cu_30>, superconducting films are known as promising c-axis-correlated pinning centers. We fabricated SmBa_2Cu_3O_y, (SmBCO) films with BZO nanorods by a low-temperature growth technique (LTG-SmBCO+BZO films). With decreasing substrate temperature of the upper layer 7_s~(upper) in LTG-SmBCO+BZO films, the diameter of BZO nanorods decreased and their number density increased, leading to a high matching field BΦ. Also, the considerable upturn shifts in the irreversibility field line and plateau regions in the magnetic field dependence of critical current density J_c were observed in the range from BΦ 3 to BΦ. These results indicate that a Bose-glass-like state of vortices localized on BZO nanorods emerges, after overcoming the vortex glass state of vortices, which are frozen on inherent pointlike disorders within the films in this magnetic field range. With this technique, it is possible to tune the flux pinning properties.