Rhombohedral ${\mathrm{CoTiO}}_3$ is a Dirac-type antiferromagnet with unique nodal magnetic dynamics, a strong Zeeman-phonon effect, and multiple spin-orbital excitations. The intricate interaction between these excitations makes it difficult to precisely understand its properties. We report the observation of strong spin-phonon coupling for several phonon modes, as well as the Zeeman splitting of the degenerate phonon modes with $E_g$ symmetry. These effects were observed in magnetic fields applied perpendicular to and within the $ab$-plane, and they evidence a phonon magnetic moment reaching up to a giant value of 1.63 ${\mu }_B$. Some of these modes experience extremely strong coupling with spin-orbital excitations of the ${\mathrm{Co}}^{2+}$ ions, manifested as avoided crossings, which leads to an underestimated magnitude of the phonon splitting at low fields. Both acoustic and optical magnon branches were observed in the antiferromagnetic phase, along with a two-magnon continuum within the 10–22 meV range, closely reflecting the magnon density of states. Observation of new magnetic modes above the spin-orientation transition at 17 T challenges the applicability of the flavor wave model to the spin dynamics in ${\mathrm{CoTiO}}_3$. Strong renormalization of the magnon and phonon modes (including zone-folded ones) suggests a low-field spin-orientation transition around 1 T within the $ab$-plane.

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• High magnetic fields
• Optical phonons
• Spin-orbit coupling
• Spin-phonon coupling
• Antiferromagnets
• Magnetic insulators
• Single crystal materials
• Raman spectroscopy