Magnetic phase transition in Fe-doped topological insulator Bi2Se3

We study the effect of Fe impurities in $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ on the magnetic phase and topological insulating property using first-principles calculations. In particular, we investigate the ferromagnetic-antiferromagnetic phase transition and the energy gap variation of surface states in Fe-doped $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$. We find that Fe-doped $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ has a ferromagnetic phase at dilute doping regime by the interplay of the band inversion and intrinsic doping. For higher Fe concentration, $>1.7\phantom{\rule{0.16em}{0ex}}\mathrm{at}.\phantom{\rule{0.16em}{0ex}}%, \mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ prefers the antiferromagnetic phase mediated by the superexchange interaction. We show that neighboring Fe impurities with antiferromagnetic ordering behave like nonmagnetic scattering centers that preserve the linear band dispersion and the in-plane spin texture of topological surface states. Our result indicates that interdependency of the magnetic phase and the band topology in transition-metal--doped topological insulators may tweak the electronic structure and topological surface states in peculiar ways.