Spin-Orbit Torques Induced by Topological Insulators of the Bi₂Te₃ Family of Materials

Van der Waals (vdW) heterostructures, including those comprising topological insulators (TIs) of the Bi₂Te₃ family of materials, have disruptive potential for magnetic random-access memory applications [1]. The boundary states of a TI can generate a non-equilibrium spin density to control the magnetization of a ferromagnet (FM) by means of the spin-orbit torques (SOTs). Recent reports have demonstrated large SOT efficiencies with TIs, however, to identify the microscopic mechanisms at play, as well as to maximize the SOT, a deep understanding and control of the properties of the TI/FM interface is needed. In this talk, I will first introduce the potential advantages of vdW heterostructures and of TIs for non-volatile spintronics memories. I will then describe the relevance of their boundary states and of preserving the quality of the TI/FM interface. I will show that the introduction of a (non-magnetic) metallic [2] or graphene [3] interlayer between the TI and the FM, when FM is a transition metal, can notably suppress Te diffusion into the FM and change the nature of the SOT and its efficiency [2]. Finally, I will argue that the discovery of vdW FMs, which can be grown as high-quality thin films [4,5], can further improve the TI/FM interface, as the weak vdW interaction between the TI and the vdW FM can limit chemical reactions, intermixing and electronic hybridization. Our recent results using Fe₃GeTe₂ demonstrate large SOTs and magnetization switching with currents densities of about 10¹⁰ A/m² [6].<br/><br/>[1] H. Yang et al., Nature 606, 663(2022)<br/>[2] F. Bonell et al., Nano Lett. 20, 5893 (2020)<br/>[3] R. Galceran et al., Adv. Mater. Interfaces 9, 2201997 (2022)<br/>[4] M. Ribeiro et al., npj 2D Mater. Appl. 6, 10 (2022)<br/>[5] J. M. J. Lopes et al., 2D Mater. 8, 041001 (2021)<br/>[6] T. Guillet et al., arXiv:2302.01101 (2023)