Ferromagnetism and superconductivity of ruthenate-cuprates RuSr2RECu2O8 (RE=Y and Er) prepared under high pressure

Abstract We report the series of ruthenate-cuprates RuSr 2 RECu 2 O 8 (RE=Y and Er), which were prepared at 1200–1300°C under 6 GPa. According to DC susceptibility measurements, ferromagnetism and superconductivity looked to coexist below ca. 40 K in both phases. However, DC resistivity was always quite high even when a sample showed a large diamagnetism in a low-temperature region. The results of EPMA analysis for RE=Y samples suggests phase separation regarding the Ru/Cu ratio in the solid solution of (Ru 1− x Cu x )Sr 2 YCu 2 O y , casting doubt for the coexistence of superconductivity and ferromagnetism.