Hydrogen reduction treatments with variations in isothermal reduction temperature, duration, and partial pressure of hydrogen (PH2) are carried out on CeO2 nanoparticles (NPs) to investigate the relationship between the surface chemical states and magnetic properties of the samples. The phenomenon of surface reduction degree dependence of the ferromagnetism of CeO2 NPs is observed. Semiquantitative calculated concentrations of surface Ce3+ ions from x-ray photoelectron spectroscopy data demonstrate that ferromagnetism does not relate to the surface oxygen vacancies but to the surface Ce3+/Ce4+ pairs. The higher the number of surface Ce3+/Ce4+ pairs, the more robust the ferromagnetism appears.
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Li et al. (2009) studied this question.
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