Observations of layer-dependent spin waves in atomically thin Ising magnets

Spin waves are collective magnetic excitations that are present in crystals with long-ranged magnetic orders. The recent discovery of atomically thin two-dimensional (2D) magnetic materials unlocks the possibilities of studying and controlling abundant spin-wave phenomena in the reduced dimensionality. In the large library of 2D magnets, few-layer CrI₃ attracts particular interest, because it consists of antiferromagnetically (AFM) coupled ferromagnet (FM) layers with an out-of-plane easy axis. Recent experiments have reported the studies of magnetic excitations on monolayer, bilayer, and bulk CrI₃ with Raman spectroscopy ^[1,2,3] and with time-resolved MOKE spectroscopy ^[4]. However, the broken translational symmetry along the out-of-plane direction in thin flakes and the lack of inversion symmetry in even but not odd layers naturally suggest a layer number dependent spin wave excitations in few-layer CrI₃, whose energy dispersions and selection rules have not been explored yet. In this presentation, I will show our experimental findings of spin waves and correspondig selection rules in few-layer CrI₃ using polarization-resolved magneto-Raman spectroscopy and discuss the magnetic field dependence of these spin waves and their responses across the critical magnetic fields.