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

• Published in: NPG Asia materials 2021-10, Vol.13 (1), Article 69
• Main Authors: An, Hyunji, Choi, Young-Gyun, Jo, Yong-Ryun, Hong, Hyo Jin, Kim, Jeong-Kyu, Kwon, Owoong, Kim, Sangmo, Son, Myungwoo, Yang, Jiwoong, Park, Jun-Cheol, Choi, Hojoong, Lee, Jongmin, Song, Jaesun, Ham, Moon-Ho, Ryu, Sangwoo, Kim, Yunseok, Bark, Chung Wung, Ko, Kyung-Tae, Kim, Bong-Joong, Lee, Sanghan
• Format: Article
• Language: English
• Subjects: 142/126; 639/301/119/544; 639/301/119/996; Annealing; Antiferromagnetism; Biomaterials; Capping; Chemistry and Materials Science; Crystal defects; Energy Systems; Ferroelectricity; Ferromagnetic materials; Induced polarization; Insulators; Leakage current; Manganese; Materials Science; Multiferroic materials; Optical and Electronic Materials; Oxygen; Permittivity; Physical properties; Room temperature; Ruthenium oxide; Strontium; Strontium compounds; Strontium oxides; Strontium ruthenium oxide; Structural Materials; Surface and Interface Science; Thin Films
• ISSN: 1884-4049; 1884-4057
• DOI: 10.1038/s41427-021-00335-7

Antiferromagnetic-paraelectric SrMnO 3 (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 ( ε r  = 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 ( ε r  = 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. Strain engineering: oxygen locks in room-temperature ferroelectricity 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 (SrMnO 3 ) 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 SrMnO 3 thin films. The team achieved this result by capping SrMnO 3 with a layer of strontium ruthenium oxide (SrRuO 3 ), 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 SrMnO 3 film to eliminate vacancy defects. We provide a conclusive demonstration of strain-induced room-temperature ferroelectricity in SrMnO 3 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 SrMnO 3 but will also inspire new directions for single-phase multiferroics.