Coexistence of magnetism and superconductivity in R_1.4Ce_0.6RuSr₂Cu₂O _10-δ (R = Eu, Sm and Gd)

The superconducting R_1.4Ce_0.6RuSr₂Cu₂O _10-δ (R = Sm, Eu and Gd) with T_c ∼ 28, 32 and 42 K are also magnetically ordered at T_N ∼ 220, 122 and 180 K, respectively, thus, T_N ≫ T_c. This is in contrast to intermetallic magnetic superconductors (such as RNi₂B₂C) in which T_c > T_N. Magnetic susceptibility and Mossbauer spectroscopy show that superconductivity is confined to the CuO₂ planes, whereas magnetism is due to the Ru sublattice. Irreversibility phenomena and magnetic anomalies, observed at low magnetic fields originate from antisymmetric exchange coupling of the Dzyaloshinsky-Moria type, and from spin reorientation of the Ru moments. The shielding fraction is about 100%, supporting the conclusion that the materials consist of a single phase, manifesting both magnetism and superconductivity at once.