Carrier mediated ferromagnetism on the surface of a topological insulator
V. N. Men'shov*, V. V. Tugushev*, E. V. Chulkov+
*National Research Centre "Kurchatov Institute", 123182 Moscow, Russia
+Departamento de Física de Materiales, Facultad de Ciencias Químicas, UPV/EHU and Centro de Física de Materiales CFM-MPC, Centro Mixto CSIC-UPV/EHU, 20080 San Sebastián, Basque Country, Spain
Abstract
We study the effect of magnetic doping at the surface of a three dimensional topological insulator
(TI) on emergence of ferromagnetic ordering at the TI-surface assuming the exchange coupling between the
Dirac fermions and the dilute magnetic ions. We show that this coupling results in an uniaxial magnetic
anisotropy with out-of-plane magnetization direction. It is found that the system under consideration is
unstable with respect to a spontaneous uniform magnetization along the easy axis, which is accompanied by
opening a gap in a spectrum of the Dirac surface states. In the framework of a mean-field approach, we study
the possibility of ferromagnetic order on the magnetically doped surface of TI at different temperatures and
positions of the chemical potential.