Origin of the saw-tooth torque in spin-orbital-coupled magnets: Application to α-RuCl₃

Honeycomb Kitaev candidate materials based on 4d⁵ and 5d⁵ metals have been recently shown to commonly display a distinct saw-tooth angular dependence of the magnetic torque over a wide range of magnetic fields. By a combination of density functional theory calculations, exact diagonalization and semiclassical considerations, we show here that bilinear anisotropic interactions and/or g-anisotropy are each sufficient to explain the observed torque response, which may be distinguished on the basis of high-field measurements.
We argue that these finding unify the understanding of magnetic torque experiments in a variety of Kitaev candidate materials.