Room-Temperature Magnetism of Ceria Nanocubes by Inductively Transferring Electrons to Ce Atoms from Nearby Oxygen Vacancy

Abstract

Ceria (CeO2) nanocubes were synthesized by a hydrothermal method and weak ferromagnetism was observed in room temperature. After ultraviolet irradiation, the saturation magnetization was significantly enhanced from ~3.18 × 10−3 to ~1.89 × 10−2 emu g−1. This is due to the increase of oxygen vacancies in CeO2 structure which was confirmed by X-ray photoelectron spectra. The first-principle calculation with Vienna ab-initio simulation package was used to illustrate the enhanced ferromagnetism mechanism after calculating the density of states (DOSs) and partial density of states (PDOSs) of CeO2 without and with different oxygen vacancies. It was found that the increase of oxygen vacancies will enlarge the PDOSs of Ce 4f orbital and DOSs. Two electrons in one oxygen vacancy are respectively excited to 4f orbital of two Ce atoms neighboring the vacancy, making these electron spin directions on 4f orbitals of these two Ce atoms parallel. This superexchange interaction leads to the formation of ferromagnetism in CeO2 at room temperature. Our work indicates that ultraviolet irradiation is an effective method to enhance the magnetism of CeO2 nanocube, and the first-principle calculation can understand well the enhanced magnetism.

Enhanced Photocatalytic Activity of Nanoparticle-Aggregated Ag–AgX(X = Cl, Br)@TiO2 Microspheres Under Visible Light

“…( 1 – 5 ) [ 13 , 34 ], which might help to photochemical decomposition. It is just similar to the research by Hu group that two electrons in one oxygen vacancy in CeO 2 are, respectively, excited to two Ce atoms neighboring the vacancy [ 35 ]. However, some researchers proposed that plasma resonance absorption of metallic Ag (or Pd) on the surface of semiconductor contributes to the effective visible absorption and segregation of electron/hole pairs, which results in the higher photocatalytic activity [ 9 , 11 , 12 ].…”

Reduction of dopant ions and enhancement of magnetic properties by UV irradiation in Ce-doped TiO2

“…On the other hand, it is possible that the intrinsically non-magnetic CeO 2 may undergo magnetic phase transition when oxygen vacancy defects (V O ) are introduced to the material. As reported in a recent paper, UV-irradiated CeO 2 indeed demonstrates enhanced room-temperature ferromagnetism 6 . UV irradiation is thought to generate oxygen vacancies, converting a substantial fraction of constituent Ce 4+ into subvalent Ce 3+ and thus enhancing ferromagnetic ordering in the ceria sample.…”

Radiative/Nonradiative Recombination Affected by Defects and Electron–Phone Coupling in CdWO4 Nanorods

“…In Figure (b), two distinct peaks at 404.6 and 411.4 eV are assigned to Cd 3d 5/2 and Cd 3d 3/2 core level, which can be used as a fingerprint to identify the presence of Cd 2+ . , Figure (c) shows a W 4f spectrum of the sample, which can be divided into four peaks by Gaussian fitting. The peaks at 35.5 and 37.6 eV are assigned to W 4f 7/2 and W 4f 5/2 core levels, which can be used as a fingerprint to identify the presence of W 6+ , while the fitting peaks centered at 34.6 and 36.6 eV are related to the W 4f 7/2 and W 4f 5/2 core level, indicating W 5+ . − As is shown in Figure (d), the peaks with binding energy of 530.2 and 531.1 eV are ascribed to O 2– ions and oxygen deficit of the sample, respectively. − The quantification of XPS peaks implies that the sample contains oxygen vacancy in Figure (d), which might act as donors for trapping charge carriers. In order to discuss the existence of W 5+ in the prepared samples, we conduct XPS analysis and have calculated the atomic ratio of Cd/W/O from the XPS intensity by evaluating the peak area under the Cd 3d, W 4f and O 1s curves with using sensitivity factors.…”