Ferroelectric ferrimagnetic double perovskite oxides design for optoelectronics

Magnetoelectric multiferroic semiconductors offer great promise for applications in magnetic storage, optoelectronics, and advanced spintronics. These materials require strong magnetization, polarization, a moderate energy gap ($1.5\phantom{\rule{0.16em}{0ex}}\text{eV}<{E}_{g}<3\phantom{\rule{0.16em}{0ex}}\text{eV}$), and high transition temperatures for both ferroelectric and ferromagnetic properties. This paper investigates six double perovskite oxides (DPOs), ${AA}^{\ensuremath{'}}{\mathrm{FeOsO}}_{6}$ ($A$ = Na, K, Rb; ${A}^{\ensuremath{'}}$= La, Y), as potential candidates. We used density functional theory to find that DPOs exhibit a polar $\mathrm{P}{2}_{1}$ phase with an ${a}^{\ensuremath{-}}{a}^{\ensuremath{-}}{c}^{+}$ tilt pattern. The polarization results from the noncancellation of layered polarization between $A\mathrm{O}$ and ${A}^{\ensuremath{'}}\mathrm{O}$ layers, which can be switched by altering their relative displacement. The strong antiferromagnetic coupling between ${\mathrm{Fe}}^{3+}$ ($S$ = 5/2) and ${\mathrm{Os}}^{5+}$ ($S$ = 3/2) leads to a stable ferrimagnetic ground state. These materials demonstrate semiconducting properties with a band gap ${E}_{g}\phantom{\rule{0.28em}{0ex}}<$ 3 eV and strong absorption in both the visible and ultraviolet regions. Ab initio molecular dynamics simulations show that the ferroelectric polarization switching temperatures exceed 300 K, making these materials suitable for room-temperature applications.