**2.1 Crystal structures**

**CrX3 (X = Cl, Br, I).** Chromium trihalides are substances in which vdW interfaces between layers X-Cr-X are dominant [28]. Within each layer, the chromium trihalides are isostructural and consist of a honeycomb structure of edge-sharing octahedral, with central chromium coordinated to six monovalent halide anions at the corner, as shown in **Figure 1a** [24, 29, 30]. Besides, these layers stack in monoclinic phase at a high temperature with space group *C*2/m: CrCl3 (above 240 K) [31–33], CrBr3 (above 420 K) [33] and CrI3 (above 220 K) [30]. On the other hand, these layers stack in rhombohedral phase with space group *R* **3** at a low temperature, as shown in **Figure 1b**. Thus, bulk CrX3 crystals are in the low-temperature rhombohedral crystallographic phase at room temperature [25]. **MPS3 (M = Fe, Ni, Mn).** The transition metal phosphorous trisulfides share a defining common structural feature such that (P2S6) 4− anion sublattice appears within each layer crystal. The honeycomb arrangement of the transition metal ions is distributed around (P2S6) 4− bipyramids, as show in **Figure 2a** [36–39]. **CrSBr** shows a layered crystal structure with vdW interactions, in which each layer is made of two buckled planes of CrS sandwiched between Br sheets and magnetic Cr3+ ions form a rectangular lattice, as shown in **Figure 3a** [40, 43, 44]. The crystal symmetry remains unchanged between 15 and 300 K [45]. **CrPS4** possesses a monoclinic symmetry with C2/m space group, in which puckered layers of S atoms are in hexagonal close packing parallel to the *a*-axis and the Cr atoms form a square lattice [46, 47]. In each layer, the Cr atom is surrounded by six S atoms, resulting in this distorted CrS6 octahedron. The P atom is coordinated in the center of three CrS6 octahedra. The weak vdW force is between sulfur layers, as shown in **Figure 4a** [49–51].
