Critical Fluctuations Induced g-factor Anisotropy in the Two-Dimensional Ferromagnetic Insulators CrXTe3 (X=Si, Ge)

Abstract

Recent discoveries of magnetic van der Waals (vdW) materials provide the ideal platform for exploring intrinsic two-dimensional (2D) magnetism down to the 2D limit and potential opportunities for new spin-related applications. However, according to Ginzburg criterion, 2D magnetism is associated with strong intrinsic magnetization fluctuations, which will break down the approximation of mean field theory in the neighborhoods of critical points [1]. In this talk, we will show the evidence for the magnetization-fluctuation-induced effective g factor anisotropy in the 2D ferromagnetic insulators CrXTe3 (X = Si, Ge) by means of ferromagnetic resonance (FMR). After deriving the classical and quantum models of magnetic resonance [2, 3], we confirm the dramatic anisotropic shift of the measured g factor to originate from fluctuations with anisotropic interactions. The deduction of the g factor behind the fluctuations is consistent with the spin-only state (g≈2.050(10) for CrSiTe3 and 2.039(10) for CrGeTe3). In addition, we will show that the abnormal enhancement of g shift, supplemented by specific heat and magnetometry measurements. We believe the results presented in this talk strongly suggest that CrSiTe3 exhibits a more typical two-dimensional nature than CrGeTe3 and may be closer to the quantum critical point. **