  The electronic and magnetic properties of iron-doped topological insulator
Bi1.84-xFe0.16CaxSe3 single crystals were studied. By co-doping Fe and Ca
atoms, ferromagnetic bulk states with different carrier density (from n-type to
p-type) were obtained. Effective magnetic moments for each Fe atom was
estimated as small as about 0.07$\mu$B. Magnetic and non-magnetic phases
separation was observed in all samples. Our results suggest that the bulk
ferromagnetism in Fe-doped Bi2Se3 is not intrinsic and regardless of carrier
density.
