Co-doping induced coexistence of superconductivity and ferromagnetism in Bi3.9Co0.1O4S3

• Bi4O4S3 is a new discovered layered superconductor. Some doping effects, such as Ag, Cu, and Pb, are studied, the superconductivity is suppressed in these doping samples. We doped the Ni magnetic ions to the system, it is interesting that the superconductivity is not suppressed in x = 0.1 sample. Meanwhile, the coexistence of the superconductivity and magnetism is observed in the samples from the M-vs. –H loops.

The effects of Co doping on the physical properties of the Bi4O4S3 system was studied. We discovered that stable Bi3.9Co0.1O4S3 compound exhibits both long-range ferromagnetism and enhanced superconductivity with thermodynamic evidences for Tc ∼ 5.5 K. We found that there is an anomalous feature which represents superconducting transition in the hysteretic M-vs.-H loops for Bi3.9Co0.1O4S3 at T = 3 K.