Spin-Orbit Torques in Mn₃Sn and FeSn Topological Semimetals

Recently discovered topological materials are promising candidates for efficient manipulation of magnetic memory and logic devices due to their exotic transport features. Topological band structures of these materials provide spin momentum locking which can generate large spin-orbit torques (SOT). Recent studies have shown that topological insulators (TIs) can generate significantly larger SOT in comparison with that by common heavy metals, due to their surface Dirac state with spin-momentum locking (1). However, SOT’s observed in these materials thus far are limited by their symmetry to lie in the film plane (2) and cannot efficiently manipulate magnetic moments of ferromagnets with perpendicular magnetic anisotropy, which are required for high-density applications.

A new class of topological materials called topological semimetals (TSMs), have not only topological bulk states but also surface Fermi arc states with unusual spin-momentum locking. Both bulk and surface states can generate large SOT whose characteristics are altogether different from that in common heavy metals and possibly TIs (3). Our work on Mn₃Sn and FeSn Topological semimetals have shown additional contributions to the signal coming from SOTs in harmonic hall measurements. The results suggest that these signals may be generated from unusual spin polarizations.

 

 

 

1. 1. Mellnik, A. R. et al. “Spin-transfer torque generated by a topological insulator”. Nature 511, 449–451 (2014).
   
   2. Garello, K. et al. “Symmetry and magnitude of spin-orbit torques in ferromagnetic heterostructures.” Nat. Nanotech. 8, 587–593 (2013).
   
   3. S.  Shi et.al, “All-electric magnetization switching and Dzyaloshinskii–Moriya interaction in WTe2/ferromagnet heterostructures”, Nat. Nanotechnol. 2019, 14, 945.