Temperature-controlled strong magnon coupling in the van der Waals antiferromagnet CrCl3

In van der Waals antiferromagnets, both magnetization and interlayer interactions are temperature dependent, and their combined effects significantly impact magnon dispersion. However, these effects remain largely unexplored. Here, we report the distinct temperature dependencies of the optical and acoustic magnon modes in a CrCl3 sample. We find that, below the Néel temperature, the optical mode softens with increasing temperature, while the acoustic mode remains insensitive to temperature variations, both experimentally and theoretically. We attribute this phenomenon to the opposing contributions of the easy-plane anisotropic field and the interlayer exchange interaction field on these two magnon modes. These factors jointly cause the softening of the optical mode but compensate each other in the acoustic mode. By leveraging the opposite temperature dependencies of two magnon modes, we achieve strong coupling between them through adjusting temperature. The coupling strength between these two modes increases linearly with the external magnetic field and remains insensitive to temperature variations. Our research provides new insights into the temperature-controlled magnon dynamics in van der Waals antiferromagnets and may advance the study of magnetization in two-dimensional materials and heterostructures. Published by the American Physical Society 2025