Effects of nanocrystalline target and columnar defects on flux pinning in pure and BaZrO3-doped YBa2Cu3O6+x films in fields up to 30 T

Transport properties of YBa2Cu3O6+x films prepared by pulsed laser deposition from pure and BaZrO3- (BZO-)doped nanocrystalline targets and from a microcrystalline target are investigated in pulsed magnetic fields up to 30 T. As shown by transmission electron microscopy, doping by BZO creates columnar defects of diameter 5-10 nm traversing the films in the direction of the c axis. The irreversibility line, the delocalization line, and the high-field critical current density j(c) are strongly enhanced in the films deposited from a nanocrystalline target in comparison with those deposited from the microcrystalline target. Doping with BZO further improves the irreversibility and depinning lines and increases the value of j(c). The irreversibility fields of the films prepared from the pure and from the BZO-doped nanocrystalline targets exceed 10 T at 77 K, and at 65 K the value of j(c)approximate to 10(5) A/cm(2) is observed in fields up to 22 T.