Temperature-induced spin density wave in a magnetically doped topological insulator Bi2Se3

We study the magnetic properties of Bi2Se3 doped with isoelectronic magnetic impurities. We obtain that at zero temperature the impurities order ferromagnetically, but when raising the temperature the system undergoes a first-order phase transition to a spin density wave phase before the system reaches the paramagnetic phase. The origin of this phase is the nontrivial dependence of the spin susceptibility on the momentum. We analyze the coupling of the nonuniform magnetic phase with the Dirac electronic system that occurs at the surfaces of the topological insulator.