Superconductivity and magnetism in the mixed-valence Mn doped La1.85-1.5xSr0.15+1.5xCu1-xMnxO4 system

A series of double-doped La1.85-1.5xSr0.15+1.5xCu1-xMnxO4 (0≤x≤0.2) samples with the Mn3+/Mn4+ ratio fixed at 1:1 were synthesized by the solid-state reaction method. The structural, transport and magnetic properties were studied. It is found that the doped Mn ions act as two kinds of steric states in the CuO2 planes. One corresponds to the randomly distributed and isolated Mn ions which are in a paramagnetic state. The other corresponds to the Mn ions which become adjacent with other Mn ions and form clusters. For a slight doping level, we not only observed the coexistence of superconductivity and paramagnetism, but also observed superconductivity coexisting with ferromagnetism. A ferromagnetic spin-glass state occurs and the superconductivity was suppressed for the 0.08≤x≤0.15 doping level. For x>0.2, antiferromagnetism is observed