First-principle Study of the 4d Transitional Metal Doped Topological Insulator

We study the electronic and magnetic properties of 4d transition-metal (TM) doped Bi₂Se_3. Doping was done separately at 4.0% and 16.6% concentrations using the atomic sphere approximation and the full-potential method to study the magnetic properties as a function of doping. Especially at 4.0% doping of Nb (1.77 µB/atom), Mo (2.98 µB/atom), Tc (3.50 µB/atom), and Ru (0.92 µB/atom), respectively, resulted in finite local magnetic moments. In addition to the magnetic nature of the doped alloys, Nb, Tc, and Ru-doped Bi₂Se₃ became half-metallic. The magnetism in these alloys arises from indirect interaction between magnetic moments mediated by free carriers within the layer and via Se atoms between layers. Using the Heisenberg model, we have observed significant effects of spin-orbit interaction on the exchange-coupling parameters of Nb and Ru-doped alloys. In contrast, at higher doping (16.6%), Bi₂Se₃ exhibited a metallic and non-magnetic nature, as demonstrated by the band structures and the density of states of the doped alloys.