Spin-orbit torque effect on magnetic defects in the surface of the topological insulator Bi₂Te₃

This work comprises a theoretical and computational investigation of the phenomenon of the spin-orbit torque [1] in topological insulators. In particular, we present the spin-orbit torque exerted on the magnetic moments of transition-metal impurities (Cr, Mn, Fe, and Co) that are embedded in the surface of the topological insulator Bi₂Te₃, in response to an electrical current in the surface [2]. The scattering properties of surface states off multiple magnetic impurities are studied by first-principles calculations within the full-potential relativistic Korringa-Kohn-Rostoker (KKR) Green function method [3]. The spin-orbit torque calculations are carried out combining the KKR method with the semiclassical Boltzmann transport equation. We discuss the correlation of the spin-orbit torque to spin current on the Fermi surface, analyzing the spin flux contribution to the spin-orbit torque on defects. The effect of resonant scattering is discussed, interpreting the results of different defects systems. In addition, we relate the torque to the resistivity and the Joule heat production in these systems. Finally, we find that the special characteristics of the studied system, i.e., the metallic surface states and the perpendicular spin-polarization of the surface electrons with respect to the magnetization of defects, reinforce the spin-orbit torque effect. Consequently, these systems are favorable materials for spintronic applications. We also predict that the Mn/Bi₂Te₃ is the most promising among the studied systems for application of the spin-orbit torque effect.

[1] Manchon A. et al., Rev. Mod. Phys. 91, 035004 (2019).

[2] Kosma A. et al., Phys. Rev. B 102, 144424 (2020).

[3] https://jukkr.fz-juelich.de