Strain-Engineered Tetragonal Phase and Ferroelectricity in GdMnO₃ Thin Films Grown on SrTiO₃ (001)

A previously unreported tetragonal phase has been discovered in a epitaxially strained GdMnO₃ thin films deposited on (001)-oriented SrTiO₃ substrates by radio frequency (RF) magnetron sputtering. The tetragonal axis of the films grown up to a 35 nm thickness is perpendicular to the film surface and the basal lattice parameters are imposed by the cubic structure of the substrate. Furthermore, the emergence of a spontaneous electric polarization below ~32 K points to the stabilization of an improper ferroelectric phase at low temperatures, which is not observed in bulk GdMnO₃. This work shows how strain engineering can be used to tailor the structure and properties of strongly correlated oxides.