Evidence of surface and bulk magnetic ordering in Fe and Mn doped Bi₂(SeS)₃ topological insulator

The magneto-transport, angle resolved photoemission spectroscopy (ARPES), and magnetization of Bi_2-xM_x(SeS)₃ (with M = Fe, Mn) have been investigated. In Fe-doped Bi₂(SeS)₃, the presence of both electron-mediated Ruderman–Kittel–Kasuya–Yosida (RKKY) coupling and carrier-independent van Vleck magnetism has been demonstrated. Interestingly, by varying the Fe content and temperature, the interplay between the two mechanisms for magnetic ordering has been revealed. On the other hand, in the Mn-doped sample, hole-mediated RKKY coupling is observed. Thus, a particular mechanism can be used to induce magnetic ordering in the topological insulator. Furthermore, both ARPES and magnetic studies indicate that surface magnetic ordering may or may not break the time reversal symmetry (TRS), whereas bulk magnetic ordering breaks the TRS, suggesting the potentiality of these materials for spintronic application.