Enhanced transport properties in YBa2Cu3Ox films with crossed columnar defects of various inclination angles

We have studied the effect of heavy-ion irradiation on the transport properties of YBa2Cu3Ox thin films. Columnar defects parallel to the c axis (0 degrees) and crossed columnar defects with various inclination angles (theta = +/- 10 degrees, +/- 20 degrees, and +/- 40 degrees) were introduced into films by 1.3 GeV U-ion irradiation with dose equivalent to 1 T vortex density. Transport properties including irreversibility fields, activation energies, and critical current densities have been measured in magnetic fields applied parallel to the c axis. The best transport properties were observed in samples of theta = +/- 10 degrees in most of the H-T plane we studied, consistent with the splay model. However, the relative enhancement of the critical current density in the theta = +/- 10 degrees compared to the 0 degrees sample was not as large as in the case of a single crystal suggesting that in films the point defects also play an important part in flux pinning. (C) 1997 Elsevier Science B.V.