Room-Temperature Ferroelectricity in Hexagonal TbMnO$_{3}$ Thin Films

Magnetoelectric multiferroics exhibit coupling between the ferroelectric and magnetic order parameters, allowing control of electric polarization by a magnetic field or magnetization by an electric field. This property is appealing for novel device applications but they require room-temperature functionality. Among a limited group of single-phase multiferroic materials, rare-earth manganites, such as TbMnO$_{3}$, are promising due to their strong magnetoelectric coupling. However, the ferroelectric transition temperature of TbMnO$_{3}$ in the bulk orthorhombic phase is very low. Here, we report room-temperature ferroelectricity of epitaxially-stabilized hexagonal TbMnO$_{3}$ thin films which is accompanied by significant polarization-dependent resistive switching. The first principle calculation and group theoretical analysis reveals that the ferroelectric polarization of hexagonal TbMnO$_{3}$ is associated with the lattice instability of prototypical paraelectric phase at the zone boundary and is also an improper ferroelectric similar to other manganites such as YMnO$_{3}$. Our results demonstrate a possibility to engineer new single-phase multiferroics by epitaxial growth, which broadens the range of functional materials desirable for novel electronic devices.