Fig. 5: Unit cells, phonon dispersions, and normal modes for FM and AFM stacking.
From: Distinct magneto-Raman signatures of spin-flip phase transitions in CrI3
a Comparing the unit cell for the FM and AFM stacked structures, where the AFM unit cell is doubled in the c direction. Chromium atoms are green, whereas iodine atoms are blue. b Calculated phonon dispersion showing the Raman-active modes in the FM (red, solid) and AFM (blue, dashed) stacking in bulk CrI3 in the monoclinic crystal structure. In the AFM case, the doubling of the unit cell along the c direction in real space results in the A(FM)-point folding into Γ, such that the number of modes is doubled compared with the FM case. The Γ–A distance in the AFM case is half that of the FM case. Modes that correspond to P1, \({\mathrm{A}}_{\mathrm{g}}^1\), P2, and \({\mathrm{A}}_{\mathrm{g}}^6\) are highlighted and their atomic vibrations are shown in c and d.
