Ferromagnetism in Fe-doped Bi2Se3 topological insulators with Se vacancies

• Effects of Se vacancies on structures and magnetism of Fe-doped Bi2Se3 are studied.
• Fe–Fe dopants and Fe–vSe tend to from clusters.
• For Fe–Fe dopants with two Se vacancies, an AFM to FM phase transition occurs.
• This transition is ascribed to Fe–Fe direct and electron-mediated FM interactions.

Effects of Se vacancies (vSes) on structural and magnetic properties of Fe-doped Bi2Se3 topological insulators are investigated with density-functional theory. It is found both the Fe–Fe dopants and Fe–vSe tend to form clusters. An antiferromagnetic (AFM) to ferromagnetic (FM) phase transition occurs when two Se vacancies are nearby the Fe–Fe dopants, triggered by Fe–Fe direct interactions and carrier-mediated FM interactions. Our results provide an understanding of magnetism in the magnetic topological insulators with Se vacancies.