Probing magnetic orders and stacking patterns in bilayer CrI₃ by theoretical Raman scattering

Chromium triiodide (CrI₃), a 2D van der Waals magnet, has been extensively studied due to its fascinating properties. Within each layer spins are ferromagnetically coupled with strong out-of-plane anisotropy, but between layers the spin ordering can be manipulated between ferromagnetic (FM) and antiferromagnetic (AFM) ordering by numerous ways, such as stacking pattern and applied electric/magnetic field. For bilayer CrI₃, the interlayer spin ordering is closely connected to the stacking configuration, such as the common hombohedral and monoclinic patterns. Using density functional theory, I carried out a systematic study on a variety of possible stacking patterns in bilayer CrI₃, where for each stacking both interlayer FM and AFM spin orders were considered. The calculations found that different stacking patterns and magnetic orderings lead to different symmetries and interlayer coupling strengths, which can alter Raman optical selection rules, phonon frequencies, and Raman intensities. This highlights the intricate interactions between stackings, spins, and phonons in 2D magnets. I will present a Raman spectra map of bilayer CrI₃ with different stacking patterns and spin orderings under both linearly and circularly polarized light for guiding experimental identification.