Mode-selective spin-phonon coupling in 2D layered antiferromagnets

Two-dimensional magnetic materials offer the opportunity to study and manipulate emergent collective excitations. Among these, spin-phonon coupling is one of the most important interactions correlating charge, spin and lattice vibrations. Understanding and controlling this coupling is important for spintronics applications, control of magnons and phonon by THz radiation, and for strain-driven magnetoelastic applications. Here, we uncover a resonant mode-selective spin-phonon coupling in several magnetic 2D metal thiophosphates (NiPS₃, FePS₃, CoPS₃ and MnPS₃) through multi-excitation and temperature-dependent Raman scattering measurements. The phonon mode, which is a Raman-active out-of-plane vibrational mode (~ 250 cm^-1 or 7.5 THz), exhibits an asymmetric Fano lineshape with its asymmetry proportional to the spin-phonon coupling. Our measurements reveal the coupling to be the highest in NiPS₃, followed by FePS₃ and CoPS₃, and least in MnPS₃. These differences are attributed to the metal-sulfur interatomic distances, which are the lowest in NiPS₃, followed by CoPS₃, FePS₃ and MnPS₃ Finally, the spin-phonon coupling is also observed in exfoliated materials, with a slight reduction between 20-30% in the thinnest flakes compared to the bulk crystals.