Anomalous spin dynamics in a two-dimensional magnet induced by anisotropic critical fluctuations

We investigate the temperature dependence of $g$ factor in two-dimensional (2D) ferromagnet ${\mathrm{CrSiTe}}₃$ by combining three-dimensional vector-ferromagnetic resonance (FMR) experiments. It is shown from the angular dependence that the dramatic $g$ shift near critical temperature originates from the interplay of enhanced magnetic fluctuations and anisotropic spin interactions in 2D magnetism. The crossover from isotropic to anisotropic $g$ factor for $T\ensuremath{\rightarrow}{T}_c$ yields anomalously parallel pumped excitations. In the critical regime, the field suppression of critical fluctuations is associated with the field dependence of $g$ shift. Furthermore, the results of FMR $g$ shift are scaled by susceptibilities and spontaneous magnetization obtained from magnetometry measurements, which show good agreement with the universality class of the 2D Ising model.