Detailed study on the role of oxygen vacancies in structural, magnetic and transport behavior of magnetic insulator: Co-CeO2

Room temperature ferromagnetism in polycrystalline CoxCe1-xO2-delta (0.001 <= x <= 0.10) bulk samples has been investigated. Annealing in the forming gas transformed the as-prepared paramagnetic into a ferromagnetic insulating material with over two orders of magnitude enhancement (from 3.7 x 10(-2) to 1.24 mu B/Co) in the magnetization. Structural characterization of both the as-prepared and H-2-treated samples showed a single phase material. The incorporation of Co with the formation of oxygen vacancies in the oxide lattice was revealed by x-ray photoelectron spectroscopy (XPS). The presence of oxygen vacancies is indicated by the existence of mixed valence states of cerium (Ce4+ and Ce3+) in the high resolution XPS 3d spectrum. The role of the donor defects (oxygen vacancies) has been verified through the removal of oxygen vacancies. The ferromagnetic insulating ground state has been explained in terms of the interaction of the F+ center and 3d magnetic cations. The connection between magnetic properties, electronic structure of the magnetic impurity and donor defect has been established. First principle calculations have been performed using the full potential linearized augmented plane wave method within the density functional theory (DFT) framework; these support our experimental findings. Both the experiment and calculations reinforced the crucial role of oxygen vacancies.