Manipulating multiple order parameters via oxygen vacancies: The case of E u 0.5 B a 0.5Ti O 3-δ

Controlling functionalities, such as magnetism or ferroelectricity, by means of oxygen vacancies (${V}_{\mathrm{O}}$) is a key issue for the future development of transition-metal oxides. Progress in this field is currently addressed through ${V}_{\mathrm{O}}$ variations and their impact on mainly one order parameter. In this paper, we reveal a mechanism for tuning both magnetism and ferroelectricity simultaneously by using ${V}_{\mathrm{O}}$. Combining experimental and density-functional theory studies of $\mathrm{E}{\mathrm{u}}_{0.5}\mathrm{B}{\mathrm{a}}_{0.5}\mathrm{Ti}{\mathrm{O}}_{3{-}{\delta}}$, we demonstrate that oxygen vacancies create $\mathrm{T}{\mathrm{i}}^{3+}3{d}^{1}$ defect states, mediating the ferromagnetic coupling between the localized Eu $4{f}^{7}$ spins, and increase an off-center displacement of Ti ions, enhancing the ferroelectric Curie temperature. Finally, the dual function of Ti sites also promises a magnetoelectric coupling in the $\mathrm{E}{\mathrm{u}}_{0.5}\mathrm{B}{\mathrm{a}}_{0.5}\mathrm{Ti}{\mathrm{O}}_{3{-}{\delta}}$.