  High quality chromium (Cr) doped three-dimensional topological insulator (TI)
Sb2Te3 films are grown via molecular beam epitaxy on heat-treated insulating
SrTiO3(111) substrates. We report that the Dirac surface states are insensitive
to Cr doping, and a perfect robust long-range ferromagnetic order is unveiled
in epitaxial Sb2-xCrxTe3 films. The anomalous Hall effect is modulated by
applying a bottom gate, contrary to the ferromagnetism in conventional diluted
magnetic semiconductors (DMSs), here the coercivity field is not significantly
changed with decreasing carrier density. Carrier-independent ferromagnetism
heralds Sb2-xCrxTe3 films as the base candidate TI material to realize the
quantum anomalous Hall (QAH) effect. These results also indicate the potential
of controlling anomalous Hall voltage in future TI-based magneto-electronics
and spintronics.
