Layered materials with magnetic properties persisting down to the monolayer 2D limit have recently emerged as platforms to investigate and manipulate exotic magnetic ground state in low dimensional systems. Within this broad family of layered systems, FePS₃ is an antiferromagnetic material with a critical temperature T_N=130 K below which neighboring magnetic moments align in an antiparallel manner. The interest in this story is in the fact that magnons, magnetic excitations of a spin lattice, are doubly degenerate in antiferromagnetic systems. We have used high pressures up to 8 GPa to tune the phonon spectrum of bulk FePS₃  in resonance with the doubly degenerate magnon and we have revealed a very peculiar coupling between these 3 different modes. For every magnon-phonon energy detuning, we can identify the magnon modes through their coupling to an external magnetic field, as is presented in Fig. 1. We show that magnons in this bulk material are mainly intralayer excitations and that decreasing the amplitude of the van der Waals gap, the inter layer distance, doesn’t influence the magnetic properties.

Reference – Amit Pawbake, Thomas Pelini, Alex Delhomme, Davide Romanin, Diana Vaclavkova, Gerard Martinez, Matteo Calandra, Marie-Aude Measson, Martin Veis, Marek Potemski, Milan Orlita, and Clement Faugeras, ACS Nano 16, 8, 12656 (2022)

Figure 1 – Magneto-Raman scattering response of buk FePS₃ at different pressure values. P_1-4 are the phonon modes while M_+/- are the two degenrrate antiferromagnetic magnon modes.