Raman scattering in antiferromagneticFePS3andFePSe3…

Raman spectra of iron phosphorus trichalcogenide crystals (FeP${X}_{3}$,X=S,Se) are measured, and a compilation of the peak frequencies is given. The spectral features due to first-order phonon Raman scattering are analyzed and assigned. At low temperatures in iron phosphorus trisulfide the vibrational Raman-scattering efficiency displays an anomalous enhancement and new structures appear. The temperature dependence of the integrated intensity, bandwidth, and frequency of the Raman peaks is studied and correlated with the antiferromagnetic ordering. It is found that the spin superstructure produces a folding of the phonon dispersion curves into the center of the Brillouin zone and activates new phonon modes in the Raman spectrum.