The vibrational properties of CrI3 single crystals were investigated using Raman spectroscopy and were analyzed with respect to the changes of the crystal structure. All but one mode are observed for both the low-temperature R3 and the high-temperature C2/m phase. For all observed modes the energies and symmetries are in good agreement with DFT calculations. The symmetry of a single-layer was identified as p31/m. In contrast to previous studies we observe the transition from the R3 to the C2/m phase at 180 K and find no evidence for coexistence of both phases over a wide temperature range.

We present the Raman scattering results on layered semiconducting ferromagnetic compound CrSiTe3. Four Raman active modes, predicted by symmetry, have been observed and assigned. The experimental results are supported by DFT calculations. The self-energies of the A 3 g and the E 3 g symmetry modes exhibit unconventional temperature evolution around 180 K. In addition, the doubly degenerate E 3 g mode shows clear change of asymmetry in the same temperature region. The observed behaviour is consistent with the presence of the previously reported short-range magnetic order and the strong spin-phonon coupling.

We present Raman spectroscopy measurements of van der Waals bonded ferromagnet Fe3−xGeTe2, together with lattice dynamics. Four out of eight Raman active modes are observed and assigned, in agreement with numerical calculations. Energies and line-widths of the observed modes display unconventional temperature dependence at about 150 K and 220 K followed by the non-monotonic evolution of the Raman continuum. Whereas the former can be related to the magnetic phase transition, origin of the latter anomaly remains an open question.