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

Abstract Ca-free Hg-based double-layered cuprates with Sr ions separating the two CuO 2 planes, Hg(Sr Ba) 2 SrCu 2 O y and its metal-substituted analogue of (Hg, M )(Sr Ba) 2 SrCu 2 O 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 ( J c ) and irreversibility field ( B irr ) , 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 CuO 2 planes does not significantly impact the temperature dependence of B irr . Notably, we found that (Hg, Re)Sr 2 SrCu 2 O y has an irreversibility line as high as that of the reported triple-layered (Hg, Re)Sr 2 Ca 2 Cu 3 O y cuprate.