Coexistence of magnetism and superconductivity in the iron containing FeSr2YCu2O7.57 cuprate as studied by μSR

Substitution of copper by iron in the charge reservoir block of the YSr2Cu3O6+δ (YSCO) cuprate superconductor brings out an appealing insight on the interplay between superconductivity and magnetism. In the resulting FeSr2YCu2O7+δ (Fe-1212) materials, FeO1+δ layers and CuO2 bi-layers are alternated along the stacking direction, in close analogy to the RuSr2GdCu2O8 (Ru-1212) ferromagnetic superconductor. For the FeSr2YCu2O7.57 compound, both BVS calculations and spectroscopic data reflect a high doping level in the superconducting planes of pCuO2 ∼ 0.30, placing this cuprate on the overdoped region of the conventional phase diagram for cuprate superconductors. Nonetheless, iron cations in the charge reservoir block (CRB) are quite oxidized, reaching a high formal oxidation state of Fe3.6+. This highly doped FeSr2YCu2O7.57 cuprate is superconducting below Tc = 30 K and, from our muon spin relaxation spectroscopy (μSR) study, the presence of magnetic interactions has been substantiated. Most interestingly, the coincidence of the onset of the magnetic interactions with the superconducting critical temperature suggests a complex interplay between magnetism and superconductivity in this overdoped cuprate.