Using density functional theory together with Monte Carlo simulations, we demonstrate that epitaxial strain, both compressive and tensile, attenuates the spin frustration of double perovskite ${\mathrm{Sr}}_2\mathrm{Fe}\mathrm{Os}{\mathrm{O}}_6$ to significantly enhance the critical temperature to 310 K, enabling room-temperature applications. We discover under tensile strain a tetragonal ($I4/m$)-to-monoclinic ($P{2}_1/n$) structural transition concomitant with an antiferromagnetic-to-ferrimagnetic transition. Furthermore, an indirect-to-direct band gap transition is observed with the valence and conduction states localized on different transition metal sublattices, opening a route to efficient electron-hole separation upon photoexcitation.

• Received 3 May 2020
• Revised 3 November 2020
• Accepted 4 January 2021

DOI:https://doi.org/10.1103/PhysRevB.103.024426