Anomalous second ferromagnetic phase transition in Co0.08Bi1.92Se3 topological insulator

We report the observation of ferromagnetism in topological insulator Co0.08Bi1.92Se3 single crystal. The structural, magnetic, and microstructure properties of Co0.08Bi1.92Se3 are investigated. The existence of complicated ferromagnetic ordering, indicates the anomalous second ferromagnetic phase transition below 30 K. Well-defined ferromagnetic hysteresis in the magnetization was found in the sample. The origin of bulk ferromagnetism in Co0.08Bi1.92Se3 is concerned with three aspects: Co cluster, RKKY interactions, and the spin texture of Co impurities.