High-Mobility Sm-Doped Bi 2 Se 3 Ferromagnetic Topological Insulators and Robust Exchange Coupling

Here we prepare a new type of diluted magnetic semiconductor (Sm$_{x}$Bi$_{1-x})_{2}$Se$_{3}$Te$_{y}$. It reaches an anistropic ferromagnetic phase at x$=$0.05, which exhibits a Curie temperature of around 50K and a typical coeric field of 0.05T. Its magnetic strength and carrier density can be tuned by controling the dopant ratio of Sm and Te separately. Robust ferromagnetism is demonstrated by the fact that electronic control makes no significant influence on the Curie temperature. The density functional theory calculation supports the ferromagnetism origin from the Sm atoms. The carrier density is \textasciitilde 10$^{18}$/cm$^{3}$ and the mobility is over 18000cm$^{2}$/V s with the pronounced schubnikov de Haas oscillations. This suggests it is a high-mobility candidate of magnetic topological insulators. (\textit{Advan. Mater. 201501254(2015)})