Effect of controlled densities of columnar defects on pinning parameters in YBa2Cu3O7-δ thin films

We have studied the effect of the densities of columnar defects on pinning parameters in YBa2Cu3O7-delta thin films prepared by the PLD method with the transport measurements. In order to produce the defects artificially in a controlled manner, the heavy-ions were irradiated onto the films. The critical current density J(c) increases with the doses of the irradiation due to the introduction of the strong pinning sites into samples. The dynamic critical exponent z, which is also one of the pinning parameters in the percolation model, increases with the densities of the irradiation defects. It should be noted that the values of z abruptly increase near a third part of the matching magnetic field, which is independent on the fluence of the irradiation. These results could be described by the percolation model as a variation of pinning strength distribution affected from the induced defects. (c) 2005 Elsevier B.V. All rights reserved.