Lattice dynamics and in-plane antiferromagnetism in MnxZn1−xPS3 across the entire composition range

Abstract

Alloyed MnxZn1−xPS3 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 MnxZn1−xPS3 and establish x≥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 ZnPS3 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 ZnPS3 and Zn-rich MnxZn1−xPS3.