Abstract:

Antiferromagnets exhibit high-speed spin responses in the terahertz frequency range and robustness against external magnetic fields, making them promising for nextgeneration high-speed, high-density spintronic devices. Recently, two-dimensional van der Waals magnetic systems, which possess rich antiferromagnetic ground states, have gained significant attention and serve as ideal platforms for studying low-dimensional antiferromagnetic physics. Detecting and controlling ultrafast spin dynamics in two-dimensional antiferromagnetic systems will lay the foundation for high-speed spintronic device applications. Antiferromagnets have no net macroscopic magnetization, making traditional optical methods, such as magneto-optical effects, challenging for detecting antiferromagnetic order in equilibrium states. However, in non-equilibrium states, the instantaneous magnetization generated by antiferromagnetic spin dynamics allows the use of time-resolved magneto-optical Kerr effect to detect coherent spin precession in antiferromagnets. Additionally, techniques such as linear dichroism spectroscopy, terahertz emission spectroscopy, and second harmonic generation have been employed in studying the dynamics of two-dimensional antiferromagnets. This paper introduces recent experimental progress on ultrafast spin dynamics in two-dimensional van der Waals antiferromagnetic systems, and briefly describes the coherent magnon excitations and corresponding mechanisms in two-dimensional antiferromagnets, including inverse magneto-optical effects/stimulated Raman scattering, orbital excitations, and exciton coupling. Furthermore, this paper discusses the critical slowing down of spin dynamics due to spin-lattice coupling effects and the amplification of coherent acoustic phonons.

Key words: antiferromagnet, van der Waals material, spin dynamics, magnon