Tailoring magnetic doping in the topological insulator Bi ₂Se₃

We theoretically investigate the possibility of establishing ferromagnetism in the topological insulator Bi₂Se₃ via magnetic doping of 3d transition metal elements. The formation energies, charge states, band structures, and magnetic properties of doped Bi₂Se₃ are studied using first-principles calculations within density functional theory. Our results show that Bi substitutional sites are energetically more favorable than interstitial sites for single impurities. Detailed electronic structure analysis reveals that Cr and Fe doped materials are still insulating in the bulk but the intrinsic band gap of Bi₂Se₃ is substantially reduced due to the strong hybridization between the d states of the dopants and the p states of the neighboring Se atoms. The calculated magnetic coupling suggests that Cr doped Bi₂Se₃ is possible to be both ferromagnetic and insulating, while Fe doped Bi₂Se₃ tends to be weakly antiferromagnetic.