Current-induced switching of ferromagnetic surface states of topological insulators proximitized by 2D ferromagnets

Spin-momentum locked surface states in topological insulators (TIs) are an ideal platform for spin-related novel functionalities, such as quantum anomalous Hall effects and efficient charge-to-spin conversion. Whereas such functionalities are accomplished by making TIs magnetic through impurity doping or proximizing with magnets, these ways would lead to low effeciency of magnetic control or suppression of the anomalous Hall effect, respectively, possibly due to inhomogenious nature of doping or weak/non-uniform coupling between TI and ferromagnets. To realize efficient coupling between the topological surface states and ferromagnetism, it is essential to find proper materials proximitizing the topological surface states. In this work, by employing molecular beam epitaxy, we fabricate heterostructures consisting of (Bi_1-xSb_x)₂Te₃ and 2D ferromagnets such as Cr₂Ge₂Te₆ [1], Fe₃GeTe₂ [2], and (Zn_1-yCr_y)Te [3]. We establish the magnetic proximity coupling at the well-defined hetero-interface supported by van der Waals force between the two layered materials by observing spatial distributions of elements and magnetization with microscopy and neutron reflectometry techniques and a large (quantum) anomalous Hall effect in transport measurements [3,4]. Then we demonstrate current-induced switching of the ferromagnetic topological surface states via spin-orbit torques [2,5]. These results may facilitate an electrical control of dissipationless topological-current circuits.

[1] M. Mogi et al. APL Mater. 6, 091104 (2018). [2] R. Fujimura et al. Appl. Phys. Lett. 119, 032402 (2021). [3] R. Watanabe et al. Appl. Phys. Lett. 115, 182401 (2019). [4] M. Mogi et al. Phys. Rev. Lett. 123, 016804 (2019). [5] M. Mogi et al. Nat. Commun. 12, 1404 (2021).