Pressure-induced charge-transfer and structural transition in hexagonal multiferroic HoMnO3

The improper ferroelectricity and frustrated magnetism observed in hexagonal rare-earth manganites are tied to Mn trimerization in the basal plane. Multiferroic properties interplay via the lattice leading to complex structural behavior with temperature and pressure. Applying hydrostatic pressure to hexagonal HoMnO${}_{3}$ induces a phase transition to a rhombohedrally distorted superstructure, accompanied by disproportionation of Mn(III) and compressibility of the basal plane. These findings reveal new insights into multiferroic manganites under extreme conditions, highlighting the complicated interactions between their properties.