ENHANCED VORTEX PINNING IN MELT-TEXTURED YBCO BY MEANS OF GOLD-ION-INDUCED DEFECTS

We have studied the effects of 235 MeV Au-197 ion implantation on crit ical current density, creep rate and irreversibility line of YBCO melt -textured bulk samples. The fluence was 1.25 . 10(11) ions/cm(2), corr esponding to a dose equivalent field of 2.5 T. We created two surface layers with correlated defects on the opposite sides of the sample, in such a way that the irradiated part was about 13% of the total volume . Such a surface irradiation caused a quite large widening of the irre versibility region in the B-T phase diagram. Critical current enhancem ents-having different behaviours as a function of field in different t emperature ranges and reaching more pronounced values at higher temper atures and fields-were found.