Alloyed ${\mathrm{Mn}}_x{\mathrm{Zn}}_{1-x}{\mathrm{PS}}_3$ samples have been grown covering the whole compositional range and studied by means of Raman spectroscopy at temperatures from 4 to 850 K. Our results, supported by superconducting quantum interference device magnetic measurements, allowed us, on one hand, to complete the magnetic phase diagram of ${\mathrm{Mn}}_x{\mathrm{Zn}}_{1-x}{\mathrm{PS}}_3$ and establish $x\ge 0.3$ as the composition at which the alloy retains antiferromagnetism and, on the other hand, to identify the Raman signatures indicative of a magnetic transition. The origin of these Raman signatures is discussed in terms of spin-phonon coupling, resulting in the appearance of low- and high-frequency phonon modes. For the alloy, an assignation of the first- and second-order modes is provided with the aid of first-principles lattice-dynamical calculations. The compositional dependence of all phonon modes is described, and the presence of zone-folded modes is shown to take place for the alloy. Finally, a comparison of the Raman spectra of ${\mathrm{ZnPS}}_3$ to other compounds of the transition metal phosphorus trisulfide family allowed us to conclude that low-frequency phonon peaks exhibit an abnormally large broadening. This is consistent with previous claims on the occurrence of a second-order Jahn-Teller effect that takes place for ${\mathrm{ZnPS}}_3$ and Zn-rich ${\mathrm{Mn}}_x{\mathrm{Zn}}_{1-x}{\mathrm{PS}}_3$.

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• Jahn-Teller effect
• Lattice dynamics
• Magnetic order
• Peierls transition
• Phonons
• Spin-phonon coupling
• 2-dimensional systems
• Crystal structures
• Density functional calculations
• Raman spectroscopy
• X-ray diffraction