Theoretical Insights into Ferromagnetism in Sm-Doped CeO2 from Hybrid Functional: Synergistic Interplay between Sm and Oxygen Vacancy.

Sm-doped CeO2 has attracted considerable attention due to its reported room-temperature ferromagnetism and potential applications in oxide-based spintronic devices. However, the microscopic origin of Sm-induced magnetism and its correlation with oxygen vacancy (V O) remain elusive. In this work, the hybrid functional method is employed to systematically investigate the electronic structure, defect energetics, and magnetic properties of Sm-doped CeO2. Results show that the Sm dopant cannot introduce spin polarization, instead strongly promotes the V O formation and preferentially forms a stable Sm-V O complex. The formation of such complex stabilizes the singly charged vacancy (V O +), which induces a Ce3+ center via localization of an unpaired electron on a neighboring Ce ion, resulting in a bound magnetic polaron (BMP). The polaron radius of BMP and the corresponding critical concentration required for BMP overlap and percolation are quantitatively evaluated, providing key insight into the conditions necessary for long-range ferromagnetic ordering. The combined first-principles calculations and percolation analysis support a physically consistent interpretation in which the experimentally observed ferromagnetism can be rationalized by BMP-mediated interactions associated with singly charged oxygen vacancies, arising from the synergistic interplay between Sm dopants and oxygen vacancies. This work offers practical design guidelines for engineering CeO2-based dilute magnetic oxides for spintronic applications.