Experimental realization of strain-induced room-temperature ferroelectricity in SrMnO3 films via selective oxygen annealing

Antiferromagnetic-paraelectric SrMnO3 (SMO) has aroused interest because of the theoretical strong coupling between the ferroelectric and ferromagnetic states with increasing epitaxial strain. In strained SMO films, the polarized state and polar distortions have been observed, although high leakage currents and air degradation have limited their experimental verification. We herein provide a conclusive demonstration of room-temperature ferroelectricity and a high dielectric constant (er = 138.1) in tensile-strained SMO by securing samples with insulating properties and clean surfaces using selective oxygen annealing. Furthermore, a paraelectricity and low dielectric constant (er = 6.7) in the strain-relaxed SMO film have been identified as properties of the bulk SMO, which directly proves that the ferroelectricity of the tensile-strained SMO film is due to strain-induced polarization. We believe that these findings not only provide a cornerstone for exploring the physical properties of multiferroic SMO but also inspire new directions for single-phase multiferroics. Thin cracks and other defects which appear in multifunctional next-generation memory materials can be suppressed through a new synthetic technique. Compounds such as strontium manganese oxide (SrMnO3) transform from insulators into electrically and magnetically active materials when fabricated into thin films that strain the crystal’s natural atom-atom separations. Sanghan Lee from the Gwangju Institute of Science and Technology, South Korea, and colleagues now report the first example of room-temperature electrical activity in strained SrMnO3 thin films. The team achieved this result by capping SrMnO3 with a layer of strontium ruthenium oxide (SrRuO3), and then annealing their new material in an oxygen-rich atmosphere. The team showed that the upper capping layer maintained the strained structure while also permitting oxygen to incorporate into the lower SrMnO3 film to eliminate vacancy defects. We provide a conclusive demonstration of strain-induced room-temperature ferroelectricity in SrMnO3 thin films by securing samples with insulating properties and clean surfaces using selective oxygen annealing. These findings will not only provide a cornerstone for exploring the physical properties of multiferroic SrMnO3 but will also inspire new directions for single-phase multiferroics.