Improvement of the flux pinning properties of Hg-based single crystals by a substitution of Ba by Sr and Hg by Pb or Re

Single crystals of mercury based cuprate superconductors were grown under h igh pressure. In some crystals, Hg was partially substituted by Re or Pb an d Ba by Sr. The Aux pinning properties of the grown crystals were measured by SQUID magnetometry, and their irreversibility lines were determined and compared. While substitutions at the mercury site did not change the irreve rsibility line significantly, a substitution of Ba by Sr enhanced the irrev ersibility field considerably. The effective mass anisotropy was determined from torque magnetometry measurements performed in the region of reversibl e magnetic behavior. Relations between the irreversibility line, the effect ive mass anisotropy and structural parameters are discussed.