Synthesis and structure of rutheno-cuprate (RE, Ce)2Sr2RuCu2O10−δ (RE = Gd, Eu) single crystals

Single crystals of the rutheno-cuprate magnetosuperconductor (RE, Ce)2Sr2RuCu2O10−δ (RE = Gd, Eu) were successfully synthesized using the self-flux method. The size of one side of the single crystals reached 100 µm for Gd and 20 µm for Eu. This is the first report of the growth of single crystals of RuRE-1222 suitable for precise X-ray structural refinement. The crystal structures were determined for (Gd, Ce)2Sr2RuCu2O10−δ specimens synthesized from starting materials with two different Ru:Cu ratios. The two crystals exhibited a similar layered structure, although the lattice parameters a and c were smaller than those reported previously for polycrystalline samples. Strong thermal vibration of oxygen on the RuO2 plane was confirmed, and no canting of the Ru octahedra was observed. The calculated density of states based on this structural analysis indicated that superconducting layers composed of the CuO2 plane and fluorite-type Gd2O2 block intersect the Fermi level and that ferromagnetic layers composed of RuO2 octahedra are located in the vicinity of the Fermi level.