Flux pinning properties and microstructure of SmBa_(2)Cu_(3)O_(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_(2)Cu_(3)O_(y) superconducting films are known as promising c-axis-correlated pinning centers. We fabricated SmBa_(2)Cu_(3)O_(y) (SmBCO) films with BZO nanorods by a low-temperature growth technique (LTG-SmBCO+BZO films). With decreasing substrate temperature of the upper layer T_(s)~(upper) in LTG-SmBCO+BZO films, the diameter of BZO nanorods decreased and their number density increased, leading to a high matching field B_(phi). 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 B_(phi)/3 to B_(phi). 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.