Improvement of critical current properties and irreversibility lines by metal substitution in Ca-free Hg-based double-layered cuprates

Ca-free Hg-based double-layered cuprates with Sr ions separating the two CuO2 planes, Hg(Sr Ba)2SrCu2O y and its metal-substituted analogue of (Hg, M)(Sr Ba)2SrCu2O y ( M=Mo , Re, and Pb), were successfully synthesized under high pressure. These novel materials exhibit bulk superconductivity at a critical temperature above 100 K. The superconducting properties, including critical current density (Jc) and irreversibility field (Birr) , were investigated through magnetic hysteresis loop measurements. Our results revealed that the M substitution with M=Mo and Re improves the J c and B irr properties, which is likely associated with a decrease in the thickness of the blocking layer. Furthermore, a comparison of the irreversibility lines between Ca-free and representative Ca-containing Hg-based compounds highlighted that the replacement of Ca by Sr in the CuO2 planes does not significantly impact the temperature dependence of B irr. Notably, we found that (Hg, Re)Sr2SrCu2O y has an irreversibility line as high as that of the reported triple-layered (Hg, Re)Sr2Ca2Cu3O y cuprate.