Phonon-excited coherent magnons and surface magnetization in Dirac magnet CoTiO₃

Understanding spin–lattice interactions, which controls spin dynamics and transport, is essential for advancing spintronic and magnonic devices. Cobalt titanate (CoTiO₃), an easy-plane antiferromagnet, has recently been identified as a host of axial phonons bearing notable magnetic moments—an effect likely tied to spin–lattice coupling. In this study, we employ time-resolved spectroscopy using terahertz excitation and a magneto-optic probe to explore how light-induced lattice dynamics influences the spin dynamics in CoTiO₃. Our measurements reveal coherent excitation of Raman-active phonons, magnon excited through phonon–polaritons, and a gradual change in probe polarization—indications of a symmetry breaking not inherent to the material's magnetic space group. The temperature dependence of these features links them to magnetic order, suggesting a role for surface-induced effects. These findings demonstrate that external symmetry breaking can significantly impact light-driven spin–lattice interactions in complex oxides.