SURFACE-BARRIER EFFECTS IN GRAIN-ALIGNED HGBA2CUO4+DELTA, HGBA2CACU2O6+DELTA, AND HGBA2CA2CU3O8+DELTA COMPOUNDS

We have studied the magnetic hysteresis and relaxation processes of gr ain-aligned HgBa2CuO4+delta, HgBa2 CaCu2O6+delta, and HgBa2Ca2Cu3O8+de lta compounds. The penetration field, H-p, the width of the magnetizat ion loops, Delta M, and the irreversibility field, H-irr, of each comp ound were found to exhibit an exponential temperature dependence [i.e. , H-p, H-irr, Delta M proportional to exp(-cT/T-0)]. This suggests tha t their magnetic relaxation is controlled by the penetration of two-di mensional pancake vortices over the Bean-Livingston surface barrier.