Using first-principles calculations, the structure and electronic properties of the room-temperature ferrimagnetic Ca2FeOsO6/Sr2FeOsO6 superlattice are investigated. We show that the superlattice hosts hybrid-improper ferroelectricity despite the fact that bulk Sr2FeOsO6 realizes an a0a0c− tilting pattern of the O octahedra. The magnitude is comparable to that of conventional ferroelectric materials and is found to increase under both compressive and tensile strain. In contrast to competing superlattices, a ferrimagnetic critical temperature above room temperature is realized. An indirect-to-direct band-gap transition is observed between n +1% and +2% strain, coming along with localization of the valence and conduction states on different transition-metal sublattices, which enables efficient electron-hole separation upon photoexcitation. The potential gradient due to the ferroelectric polarization supports the electron-hole separation and a spectroscopic limited maximum efficiency of 27% confirms excellent potential in solar cell applications. The tunable room-temperature ferroelectricity, high critical temperature of the ferrimagnetic ordering with high magnetization, and favorable photoabsorption properties of the Ca2FeOsO6/Sr2FeOsO6 superlattice open up a broad range of technological applications.
Bibliographical noteKAUST Repository Item: Exported on 2023-04-03
Acknowledgements: The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST). For computer time, this research used the resources of the Supercomputing Laboratory at KAUST.