Spin-phonon coupling and magnon scattering in few-layer antiferromagnetic FePS3

Abstract

Temperature-dependent Raman spectroscopic studies of spin-phonon (SP) coupling and magnon scattering in bulk and few-layer (FL) antiferromagnet (AFM) ${\text{FePS}}_{3}$ with N\'eel temperature (${T}_{N}$) $\ensuremath{\approx}$ 120 K were performed. Bulk and FL (2--5 atomic layers) samples show four distinct modes at room temperature between 150 and $400 {\text{cm}}^{\ensuremath{-}1}$ and a broad peak at $\ensuremath{\approx}105 {\text{cm}}^{\ensuremath{-}1}$. On lowering the temperature, three distinct phenomena are observed. First, we see the SP coupling, identified by the deviation from the usual two- or three-phonon anharmonic behavior of the higher wave number peaks ($\ensuremath{\ge}150 {\text{cm}}^{\ensuremath{-}1}$) at or below ${T}_{N}$. The strength of SP coupling can be calculated for bulk and FL flakes considering mean-field approximations. Secondly, we see the spin ordering marked by the evolution of three peaks at lower wave numbers (around $105 {\text{cm}}^{\ensuremath{-}1}$) below ${T}_{N}$ due to incommensurate magnetic cells at low temperature. Thirdly, magnon excitation in FL pristine ${\text{FePS}}_{3}$ is detected by the emergence of a distinct peak at $120 {\text{cm}}^{\ensuremath{-}1}$ ($\ensuremath{\sim}3.6$ THz) at a temperature much lower than ${T}_{N}$ ($\ensuremath{\approx}60$ K). Tracking the magnon mode in the designed van der Waals heterostructures with ${\text{Bi}}_{2}{\text{Te}}_{3}$ and ${\text{Cr}}_{2}{\text{Ge}}_{2}{\text{Te}}_{6}$ reveal interfacial electron and hole transfer from ${\text{FePS}}_{3}$, respectively. Raman spectroscopy can thus predict the magnetic transition temperature of FL magnetic insulators via SP coupling, zone-boundary phonons, and magnons. Quasi-two-dimensional AFMs and their heterostructures involving different electronic and magnetic orders may be promising candidates for ultrafast magnon transport involving magnetoelastic waves.