title: Towards understanding the electronic structure of Fe-doped CeO2 nanoparticles with X-ray spectroscopy.
abstract: This study reports on the electronic structure of Fe-doped CeO2 nanoparticles (NPs), determined by coupled X-ray absorption spectroscopy and X-ray emission spectroscopy. A comparison of the local electronic structure around the Ce site with that around the Fe site indicates that the Fe substitutes for the Ce. The oxygen K-edge spectra that originated from the hybridization between cerium 4f and oxygen 2p states are sensitive to the oxidation state and depend strongly on the concentration of Fe doping. The Ce M(4,5)-edges and the Fe L(2,3)-edges reveal the variations of the charge states of Ce and Fe upon doping, respectively. The band gap is further obtained from the combined absorption-emission spectrum and decreased upon Fe doping, implying Fe doping introduces vacancies. The oxygen vacancies are induced by Fe doping and the spectrum reveals the charge transfer between Fe and Ce. Fe(3+) doping has two major effects on the formation of ferromagnetism in CeO2 nanoparticles. The first, at an Fe content of below 5%, is that the formation of Fe(3+)-Vo-Ce(3+) introduces oxygen deficiencies favoring ferromagnetism. The other, at an Fe content of over 5%, is the formation of Fe(3+)-Vo-Fe(3+), which favors antiferromagnetism, reducing the Ms. The defect structures Fe(3+)-Vo-Ce(3+) and Fe(3+)-Vo-Fe(3+) are crucial to the magnetism in these NPs and the change in Ms can be described as the effect of competitive interactions of magnetic polarons and paired ions.
authors.affiliation: Department of Physics, Tamkang University, Tamsui, 25137, Taiwan. clchang@mail.tku.edu.tw.
authors.forename: Wei-Cheng
authors.initials: WC
authors.lastname: Wang
authors.forename: Shih-Yun
authors.initials: SY
authors.lastname: Chen
authors.forename: Per-Anders
authors.initials: PA
authors.lastname: Glans
authors.forename: Jinghua
authors.initials: J
authors.lastname: Guo
authors.forename: Ren-Jie
authors.initials: RJ
authors.lastname: Chen
authors.forename: Kang-Wei
authors.initials: KW
authors.lastname: Fong
authors.forename: Chi-Liang
authors.initials: CL
authors.lastname: Chen
authors.forename: Alexandre
authors.initials: A
authors.lastname: Gloter
authors.forename: Ching-Lin
authors.initials: CL
authors.lastname: Chang
authors.forename: Ting-Shan
authors.initials: TS
authors.lastname: Chan
authors.forename: Jin-Ming
authors.initials: JM
authors.lastname: Chen
authors.forename: Jyh-Fu
authors.initials: JF
authors.lastname: Lee
authors.forename: Chung-Li
authors.initials: CL
authors.lastname: Dong