Raman Spectroscopy of layered magnetic systems

Metal phosphorus trichalcogenides (MPX₃) have emerged as an exciting class of layered magnetic 2D materials for future spintronics. Retaining long range magnetic ordering even in the exfoliated few layers is the hallmark of 2D magnetism. Raman spectroscopy can be an effective probe to identify low-energy phonon modes and possible spin-phonon coupling in reduced dimension from bulk crystal. In this study, temperature dependent Raman Spectra of exfoliated iron phosporous trichalcogenides (FePS₃) flakes reveal a distinct shift of the large wave number phonon peaks towards higher wavenumber as temperarure decreases. A clear deviation from standard anharmonic behavior below characteristic Néel temperature (T_N) is also observed. Other low wave number symmetry modes exhibit temperature dependent non-anharmonic self-energy as a function of layer thickness below T_N, related to the strong spin-lattice interaction due to short-range magnetic order. Energies and symmetries of the observed Raman-active modes are in agreement with DFT calculations. Below T_N low wave number broad mode in the paramagnetic state(T>T_N) splits into multiple distinct modes and evolve further into a possible magnon mode. We believe these results will pave way for possible spintronic applications exploiting magnons.