Enhancement of self-field critical current density by several-tens-MeV ion irradiation in YBa2Cu3O7 films prepared by fluorine-free metal-organic deposition

An up to 63% enhancement in critical current density (J (c)) was achieved for 1 mu m thick YBa2Cu3O7 (YBCO) films at self-field at 77 K by irradiation with 24-84 MeV Au ions. This enhancement is highly unusual, since in YBCO films, J (c) at self-field (J (c) (sf)) is generally insensitive to ion irradiation, unlike J (c) in magnetic fields. Our observed film-thickness dependence of the irradiation effect and our microstructure imaging indicate that this rare observation is attributed to an extremely "clean" (i.e. less-disordered) microstructure in the top 700 nm of the layer of our 1 mu m thick films prepared via fluorine-free metal-organic deposition. Our results directly indicate that discontinuous 1D vortex-pinning centers (pins) that have the following features effectively enhance MA cm(-2)-order J (c) (sf) at 77 K of YBCO films; namely, 5-10 nm in diameter, similar to 20 nm in size along a pin track, have a similar to 20 nm gap between the pins in a pin track, and are directed in the c-axis.