Electronic structures and magnetic properties of rare-earth (Sm,Gd) DOPED Bi2Se3

First-principles calculations based on density functional theory are performed to investigate the formation energies, band structures, and magnetic properties of rare-earth (RE) metal (Sm, Gd) doped topological insulator Bi2Se3. Our results show that Bi substitutional sites are energetically more favorable for single Gd or Sm impurities. The Sm-doped Bi2Se3 shows a metallic behavior with Sm-f energy band around the Fermi level, while Gd-doped Bi2Se3 exhibits insulating property with a band gap of 0.03eV. As the electron configuration of Gd3+ is 4f7, its total orbital angular momentum is zero and only spin moment is left, while for Sm3+ the net magnetic moment is 3.65μB with the low-lying J=7/2 excited state. Further investigation on the magnetic coupling between dopants has suggested that Gd-doped Bi2Se3 tends to be paramagnetic state while Sm-doped Bi2Se3 has a possibility to be ferromagnetic metal, in which easy axis of magnetization lies perpendicular to c-axis.