Structural transformations in Type II Multiferroic and Probable Topological NontrivialInsulator MnSb₂Se₄ under High Pressure

The AB₂X₄ (where A = Fe, Mn; B = Sb, Bi; and X = S, Se, Te) family of materials has attracted the scientific community after the recent observation of the Quantum Anomalous Hall Effect in MnBi₂Te₄. Among the isostructural compounds, MnSb₂Se₄ is a type II multiferroic with strong magneto-electric coupling. It undergoes a long-range antiferromagnetic ordering at 22.5 K. Recent studies on MnSb₂Se₄ based on first-principle calculations predicted that it could be converted into Weyl semimetal at a pressure of ~ 0.85 GPa and to a 3D anti-ferromagnetic topological insulator at ~ 2.45 GPa. It is expected that S- and Se-based AB₂X₄ materials with tetradymite-like structures could exhibit pressure-induced topological quantum phase transitions. We report high-pressure Raman Spectroscopy and synchrotron X-ray diffraction studies on polycrystalline MnSb₂Se₄ till 12 GPa exploring the topological, electronic and structural phase transitions. Here the material crystallizes in the C2/m monoclinic phase. Under pressure, it shows some intriguing behavior, with some Raman modes softening and some others hardening which indicates strong anisotropy in the system. Pressure evolution of Raman modes and their full width at half maximum show slope changes at ~1.0 GPa and ~2.5 GPa. The XRD results show changes at ~1.9 GPa and at ~5 GPa with the coexistence of phases over some ranges and the transitions are reversible.