Spin texture and magnetic anisotropy of Co impurities in Bi2Se3 topological insulators

Based upon first-principles methods, we investigate the magnetic anisotropy and spin texture of Co impurities embedded at the interlayer van der Waals (vdW) spacings and onto the topmost Se network of the topological insulator Bi2Se3. The interaction of the magnetic impurity with the surface spin texture breaks time-reversal symmetry, opening up a surface band gap. For a Co atom adsorbed onto the surface, the net magnetic moment is aligned perpendicular to the surface plane, with anisotropy energy of 6 meV. On the other hand, for the Co impurity at the vdW interlayers, the net magnetic moment is aligned in plane. While pristine Bi2Se3 presents a helical spin texture in the massless surface Dirac cone and states resonant within the valence band, the presence of the Co impurity reduces the planar spin helicity of now massive Dirac fermions.