Strain-modulated Ferromagnetism And Electronic Structure Of Magnetic Doped Bi₂Se₃

Due to its robust surface states less influenced by generalimpurities, topological insulators (TIs) have attracted tremendousattention and the TI has been a hot topic in condensed matter physicsand materials science in recent years. Especially, three compoundsBi2Se3, Bi2Te3and Sb2Te3were found to be three dimensionally strongtopological insulators with large bulk gap and simple surfaceelectronic structures, which make them stand out in the numeroustopological insulator materials. On the other hand, Theferromagnetism in the topological insulator will break thetime-reversal symmetry and induce strong spin-orbit coupling gapwhich is expected to realize the quantum anomalous Hall effect(QAHE). The QAHE have been theoretically predicted andexperimentally confirmed in magnetic topological insulators (TI) in2003. However, dissipative channels resulted by small-size band gapand low Curie temperature can easily influence the observation ofQAHE. Hence, strong ferromagnetic TIs with large-size band gap needto be found in order to realize high temperature QAHE, which will bean urgent problem.In this paper we systematically investigate the electronic and magnetic properties of3d transition metal Mn and Cr dopedtopological insulator with strains by using first-principlescalculations based on the density functional theory. It is expectedthat the research results can provide a new route and a efficienttunable way for realizing high-temperature QAHE.(1)We systemically study of the magnetic properties andelectronic structures of Mn doped6QLs Bi2Se3with in-plane andout-of-plane strains. It is found that out-of-plane tensile strain notonly improve ferromagnetism, but also enlarge Dirac-mass gap (upto65.6meV under6%strain) in the Mn doped Bi2Se3. More, theunderlying mechanisms of these tunable properties are alsodiscussed.(2)we systemically study of the magnetic properties of Cr dopedBi2Se3in four different doping with in-plane and out-of-plane strains.It is found that in-plane strain whether compressive strain or tensilestrain can improve ferromagnetism when Cr doped Bi2Se3of thesame quintuple layer in plane.