Effect of Copper doping in structure and Ferromagnetism of Nanocrystalline CeO₂
Kai Chung1,2*, Po-Heng Lin1, Shih-Yun Chen1, Chi-Liang Chen2, Chung-Li Dong3, Ting-Shan Chan2, Jeng-Lung Chen2
1Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan
2National Synchrotron Radiation Research Center, Hsinchu, Taiwan
3Department of Physics, Tamkang University, New Taipei City, Taiwan
* presenting author:Kai Chung, email:kai19920707@gmail.com
The relationship between defect structure and magnetic behavior of Cu-doped CeO₂ nanoparticles (NPs) was studied systematically by using spectroscopy and microscopy. These NPs were prepared by precipitation method from cerium (III) nitrate, EG and DI water. The doping level of Cu ranges from 0 to 20 at%. Crystal structure was characterized by X-ray Diffraction. The unoccupied electronic states, lattices structural distortion and hybridizations between ions were studied by X-ray Absorption Spectroscopy (XAS). Ferromagnetism was also measured by Vibrating Sample Magnetometer (VSM) at room temperature.
The evolution of defect structures of Cu doped CeO₂ NPs was different from those with trivalent dopants based on our earlier reports, for instance, rare earth ions Sm and Y. Cu ions might be found to be interstitial in the CeO₂ lattice as doping level is low while it forms second phase at surface as doping level reaches 15%. Above various form of Cu ions thus induced different type of oxygen vacancy complex. Accordingly, XAS analysis showed that the valence of Ce was not simply proportional to the concentration of Cu. In addition, room temperature ferromagnetism (RTFM) was observed of all the NPs. The mechanism of RTFM in Cu doped CeO₂ NPs were discussed via the relationship among the valence of Cu, form of oxygen vacancy complex, concentration of Ce³+, and the revealed magnetism.

Keywords: Nanoparticles, Defect, Ferromagnetism, X-ray Absorption Spectroscopy