Pinning properties in (Hg0.8Cu0.2)Ba(2)Cu0(4+delta) single crystals: relaxation and irradiation studies

Dc magnetic relaxation measurements were performed on pristine and irradiat ed Hg-1201 single crystals. In relation to the doping level, we analyse the measurements on the pristine single crystals near the fishtail line. The f ishtail effect originates from a competition between a critical current tha t increases against the magnetic field and the pinning energy which decreas es against the magnetic field. Depending on the doping level of the single crystals, the fishtail effect may be observed or not, without any correlati on with a transition of the vortex relaxation creep (plastic to elastic). The pinning properties have been modified by the introduction of columnar d efects along the c-axis by irradiation with 6 GeV Pb ions. The columnar nat ure of the induced latent tracks is probed by high-resolution electron micr oscopy. It is shown that, in the presence of correlated disorder, Hg-1201 e xhibits features similar to those previously reported in Y-123, despite a l arger electronic anisotropy.