Artificially imposed hexagonal ferroelectricity in canted antiferromagnetic YFeO3 epitaxial thin films

Antiferromagnetic YFeO3, belonging to a family of centrosymmetric orthoferrites (space group Pbnm), is known to be nonferroelectric. Here we report, contrary to this common knowledge, that an epitaxial YFeO3 thin film fabricated by adopting a hexagonal template is characterized by a six-fold hexagonal symmetry and exhibits ferroelectricity with a ferroelectric Curie temperature (Tc) of ∼460 K. According to first-principles calculations, the P63/mmc–P63cm structural phase transition at Tc by the freezing-in of the zone-boundary K3 phonon is primarily responsible for the observed room-temperature ferroelectricity and the asymmetric image orbital overlapping along the c-axis of P63cm over the Γ–M first Brillouin zone is the electronic origin of this artificially imposed ferroelectricity. For temperatures between 115 K (Néel point) and 20 K, the present thin film interestingly shows meta-magnetism-like responses.