Strain-attenuated spin frustration in double perovskite Sr2FeOsO6

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 Sr2FeOsO6 to significantly enhance the critical temperature to 310 K, enabling room-temperature applications. We discover under tensile strain a tetragonal (I4/m)-to-monoclinic (P21/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.