Investigation of the vortex confinement mechanisms in melt textured YBa2Cu3O7-x with ion-induced surface nanostructuring

In the present paper the magnetic properties of high-quality melt-textured YBa2Cu3O7-x irradiated with 2GeV gold ions are studied. The irradiation affects a surface layer of 50 μm (about 10% of the whole sample thickness), while linearly correlated columnar defects are estimated to be present up to about 46 μm. The paper is focused on the magnetic property analysis of the material before and after irradiation, as determined by the competition and/or correlation between surface columnar defects and intrinsic defects. In the intermediate- and high-temperature regions (T > 45 K), the surface columnar defects are very effective according to critical current density J c, pinning force F p, creep rate and irreversibility line measurements. In particular the detailed study of the F p versus B curves at 75 K by means of a modified Dew-Hughes model shows that, before and after irradiation, several kinds of defect are effective in difFerent field ranges. After irradiation, the columnar defects greatly modify the fuli scenario near an accommodation field lower than the dose equivalent field. This large effect could depend on the fact that, at least at higher temperatures, the strong pinning of the vortices in the surface layers induces easier confinement of the vortices trapped by volume and planar defects in deeper layers.