Magnetic studies of flux pinning in YBa2Cu3O7-x, YBa2Cu4O8 and Hg-based single crystals

The flux-pinning mechanism in YBa2Cu3O7-x, (Y-123), YBa2Cu4O8 (Y-124), HgBa2CuO4+x (Hg-1201) and HgBa2Ca2Cu3O8+x (Hg-1223) is compared. Single crystals of Y-123, Y-124 and Hg-1201 show a very pronounced fishtail effect, observed in a wide temperature range. For each compound the irreversibility field and the field at which the peak in the fishtail occurs are well described by a power-law dependence H-in/peak(T) = H-in/peak(0)(1 - T/T-c)(alpha) with very similar exponents. In Hg-1223 the pinning has a more three-dimensional character at higher temperatures, but becomes rather two dimensional at low temperatures. (C) 1998 Elsevier Science B.V. All rights reserved.