This article reports on reversible manipulation of room temperature ferromagnetism (RTFM) in nondoped bulk ${\text{CeO}}_2$ . The magnetization measurements establish that paramagnetic ${\text{CeO}}_2$ is driven to a ferromagnetic state, without change in structure, when vacuum annealed at $600°\text{C}$ . The Ce ions transform from $4+$ to $3+$ state, accompanied by evolution of oxygen vacancies $\left({\text{V}}_{\text{O}}\right)$ during the RTFM transition, as determined by x-ray photoemission. The ${\text{F}}^{+}$ centers (the electrons in singly occupied oxygen vacancies) play key role in the exchange mechanism. The transition shows complete reversibility where the RTFM is removed by removing the vacancies through re-heating the vacuum-annealed ${\text{CeO}}_2$ in air.

In this work, we demonstrate that room temperature ferromagnetism can be induced in pristine anatase ${\text{TiO}}_2$ paramagnetic bulk powder through extended hydrogenation. Defect complexes, ${\text{Ti}}^{3+}–{\text{V}}_{\text{O}}$ (${\text{Ti}}^{3+}$ ions accompanied by oxygen vacancies) are clearly identified in hydrogenated ${\text{TiO}}_2$ by combining x-ray diffraction and photoemission spectroscopy. The observed ferromagnetic ordering is reversible that can be switched between “on” and “off” by inducing or removing, respectively, these defect complex. We convincingly elucidate that the factors (i) $\text{Ti}3d–\text{O}2p$ hybridization (iii) ${\text{F}}^{+}$ centers (the electrons in singly occupied oxygen vacancies), and (iii) oxygen vacancy assisted fragmentation of grains, compositely contribute to the ferromagnetic ordering.