Magneto-Raman study of magnon and spin-orbit excitations in CoTiO₃

With a J_eff=1/2 ground state of Co²⁺ ions in a stacked honeycomb lattice, CoTiO₃ has recently been in the spotlight due to its promise of exotic magnetic behavior. Specifically, a Dirac crossing was measured in its magnon spectrum by two different groups via inelastic neutron scattering. This spectrum displays a linear crossing at the Dirac point, as well as higher energy spin-orbit excitons, coming from the J=5/2 multiplets. Thus, CoTiO₃ is a promising material to explore the properties of topological magnons.

We are reporting on our work on CoTiO₃ using temperature dependent magneto-Raman scattering. First, we follow the evolution of the Brillouin Zone center excitations of not only the optical magnon, but also several spin-orbit excitations across the magnetic transition. Our experiment provides a high-resolution measurement of these magnetic modes at k=0. Second, by applying the external magnetic field along the c-axis and along a hexagonal axis, we revealed the highly anisotropic g-factor of these magnetic excitations. Surprisingly, we measured the beginning of a magnetic field induced crossing between the acoustic and optical magnon. We use a spin wave model based on previous studies to support our data.