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

Abstract

Room temperature ferromagnetism in polycrystalline Co(x)Ce(1-x)O(2-δ) (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 × 10(-2) to 1.24 μ(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 (Ce(4+) and Ce(3+)) 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.

Toward tailored functionality of titania nanotube arrays: Interpretation of the magnetic-structural correlations

“…This change in Pauli paramagnetism implies a parallel change in the electronic density of states at the Fermi level, which can be correlated with the catalytic activity of these nanostructures for further tailoring of catalytic properties. 32,34,48 Considering the suggested magneto-catalysis correlations in the metal oxides, optimization of annealing conditions is expected to lead to enhanced photocatalytic activity of titania that originates from such magneto-structural tailoring. 6,7 …”

Sour water–gas shift reaction over Pt/CeZrO2 catalysts

“…Ce3d core-level XPS spectrum complexity has been often described, and it is due to the hybridization that occurs between cerium 4f and oxygen 2s orbitals [20,40,48,70]. Conventionally the letters U and V are used to represent peaks related to the spin-orbit splitting of Ce3d 5/2 and Ce3d 3/2 , respectively.…”

Concentration dependence of magnetic moment in Ce1-xFexO2

“…In addition to oxygen vacancies, TM doping has been shown to increase the RTFM of ceria NPs (6)(7)(8)(9)(10)(11)(12)(13). There are at least two possible mechanisms for RTFM enhancement by TM doping: creation of oxygen vacancies by introduction of a different-valance dopant into the host lattice and ferromagnetic ordering of a TM dopant.…”