Long-range magnetic orders in atomically thin ferromagnetic CrI₃ trigger new fascinating physics and application perspectives. The physical properties of two-dimensional (2D) ferromagnetism CrI₃ are significantly influenced by interlayer spacing and stacking order, which are sensitive to the hydrostatic pressure and external environments. However, there remains debate on the stacking order at low temperature. Here, we study the interlayer coupling and stacking order of non-encapsulated 2–5 layer and bulk CrI₃ at 10 K by Raman spectroscopy; demonstrate a rhombohedral stacking in both antiferromagnetic and ferromagnetic CrI₃. The opposite helicity dependence of A_g and E_g modes arising from phonon symmetry further validates the rhombohedral stacking. An anomalous temperature-dependent behavior is observed due to spin-phonon coupling below 60 K. Our study provides insights into the interlayer coupling and stacking orders of 2D ferromagnetic materials.

原子稀薄的铁磁CrI _3中的远距离磁阶引发了新的令人着迷的物理学和应用前景。二维（2D）铁磁性CrI ₃的物理性质受层间间距和堆叠顺序的影响，层间间距和堆叠顺序对静水压力和外部环境敏感。然而，关于低温下的堆叠顺序仍有争议。在这里，我们通过拉曼光谱研究了在10 K下未封装的2–5层和块状CrI ₃的层间耦合和堆叠顺序。证明反铁磁和铁磁CrI _3中的菱面体堆叠。A _g和E _g的相反螺旋度依赖性由声子对称引起的模态进一步验证了菱面体的堆叠。由于60 K以下的自旋声子耦合，观察到了异常的温度相关行为。我们的研究提供了对2D铁磁材料的层间耦合和堆积顺序的见解。