Theoretical Raman Study of In-Plane Spin–Phonon Coupling in a CrCl3 Monolayer

Raman spectroscopy is a crucial technique for characterizing two-dimensional (2D) magnetic materials, offering valuable insights into their structural and magnetic properties. This method is particularly significant in the study of chromium trichloride (CrCl₃), a material that has garnered considerable attention due to its unique magnetic behavior. In this study, by considering only the nearest neighbor exchange interactions, we systematically investigated the magnetic Raman response of 2D CrCl₃ and observed a notable frequency shift of approximately 20 cm^–1 in the E_g² Raman peak across different magnetic configurations. This shift is primarily attributed to spin–phonon coupling, thereby providing a reliable means to distinguish between various magnetic configurations. The E_g² Raman peak is associated with the collective vibrations of Cr and Cl atoms, with Cr atoms playing a dominant role in the observed differences between magnetic configurations. Even when considering more complex magnetic configurations, such as including next-nearest and third-nearest neighbor interactions, nearest neighbor exchange interactions remain the most significant. This predominance allows the E_g² peak to be effectively interpreted as a superposition of simpler magnetic configurations. Additionally, we explored the effects of external strain and carrier doping on the Raman spectrum of 2D CrCl₃. Under external biaxial strain, the E_g² peak exhibits anomalous frequency shifts. Electron doping significantly influences the Raman spectra, whereas hole doping has only minimal effects. Importantly, the in-plane spin–phonon coupling remains largely unaffected by variations in crystal thickness, crystal phase, or interlayer magnetic interactions. These findings enhance our understanding of the intrinsic spin–phonon coupling in CrCl₃ and establish a robust foundation for exploring and engineering the magnetic properties of 2D materials.