COEXISTENCE OF FERROMAGNETISM AND HIGH-TEMPERATURE SUPERCONDUCTIVITY IN Dy-DOPED BiPbSrCaCuO

The interplay of ferromagnetism and superconductivity is obviously a topic of great fundamental and practical interest. Specifically, weak ferromagnetism was recently reported to coexist with superconductivity in heavy-fermion specimens.1–3 Even more recently, the discovery that ferromagnetism exists together with superconductivity in high-temperature superconductors (HTSC) of the EuCeRuSrCuO family stimulated extreme interest. We report the coexistence of the two phenomena in a different HTSC family: Dy-doped Bi2−xPbxSr2Ca1−yDyyCu2O8+δ. Single crystal samples which clearly exhibit such coexistence below the superconducting critical temperature Tc ∼ 80 K, whereas ferromagnetism persists at least up to room temperature. The novelty and importance of the result stem not only from the intrinsic interest of the coexistence of possibly antagonistic phenomena, but also from the fact that most of the previous perovskite magnetic superconductors contain Ru. Ferromagnetism in this family of superconductors is believed to originate from the RuO sublattice, similar in structure to ferromagnetic SrRuO3. 4,5 In our samples, since there is no Ru, other mechanisms for the coexistence ferromagnetism at the rather high superconducting critical temperature would have to be reconsidered. Large-size Bi2−xPbxSr2Ca1−yDyyCu2O8+δ single crystals with y ranging from 0 to 1 were grown by a nonstoichiometric self-flux method. The starting oxides, carbonates and nitrates were prereacted and then melted at 1100◦C. The melt was cooled at a rate of 3◦C/h to 940◦C, then at 1◦C/h to 800◦C and finally at 50◦C/h to 20◦C in air. Platelike crystals with facets of size up to 5 × 5 × 0.05–0.5 mm were then extracted from the crucible. In this work, only the result from the sample with Dy ≈ 0.05 is presented. X-ray diffraction measurements were performed with both conventional tube source and synchrotron X-rays from the 5C2 beamline of the Pohang Light