Bulk superconductivity in RuGd-1212 single crystals

The occurrence of bulk superconductivity in the magnetosuperconductor GdSr2RuCu2O8−δ (RuGd-1212) remains controversial. Recently, we have successfully grown single crystals of RuGd-1212 with a size of 100 m by partial melting. Although most single crystals prepared by conventional methods do not exhibit superconductivity, the superconductivity could be improved optimizing the synthetic conditions, and subtle changes in the sintering temperature were found to influence the emergence of superconductivity. Although most of the superconducting samples contained a small amount of the impurity phase Sr2GdRuO6, superconducting RuGd-1212 single crystals were the predominant phase. Furthermore, we successfully observed an onset transition temperature (Tc-onset) of 30 K and an in-plane critical current (Ic) of 12 mA. These experimental results indicate that the obtained RuGd-1212 single crystals exhibited bulk superconductivity.