Investigation of the vortex con® nement 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 a? ects a surface layer of 50 mm (about 10% of the whole sample thickness), while linearly correlated columnar defects are estimated to be present up to about 46mm. 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 e? ective according to critical current density Jc, pinning force Fp, creep rate and irreversibility line measurements. In particular the detailed study of the Fp versus B curves at 75K by means of a modi® ed Dew-Hughes model shows that, before and after irradiation, several kinds of defect are e? ective indi?erent® eldranges.Afterirradiation,thecolumnardefectsgreatlymodifythe full scenario near an accommodation ® eld lower than the dose equivalent ® eld. This large e? ect could depend on the fact that, at least at higher temperatures, the strong pinning of the vortices in the surface layers induces easier con® nement of the vortices trapped by volume and planar defects in deeper layers.