The evolution of ferroelectricity and ferromagnetism in epitaxial and freestanding SrTiO3-σ thin films

Abstract

Tuning single-crystalline transition metal oxide to possess multi functionalities, for instance, ferroelectricity and ferromagnetism through strain and defect engineering is crucial for facilitating related functionalities that have implications for device applications. To clarify the dependence relationship between strain and defect for emergent ferroics in complex oxide, in this study, we report the ferroelectric and magnetic properties of oxygen-deficient SrTiO3-σ (STO3-σ) thin films in rigid heterostructure and freestanding forms. By an appropriate introduction of oxygen vacancies, the STO3-σ exhibits the coexistence of ferroelectricity and ferromagnetism in its rigid heterostructure, however, these features are eliminated if STO3-σ turns to the freestanding thin films via a water-dissolution of Sr3Al2O6 (SAO) sacrifice interlayer. Our experimental findings demonstrate that both ferroelectricity and ferromagnetism of STO3-σ need the stabilization of the defects by strain which enlarges the activation energy of the anionic defect suggesting a promising multiferroic engineering method. Meanwhile, our study also provides valuable information on flexoelectric/flex magnet devices.