Relationship between the surface chemical states and magnetic properties of CeO_2 nanoparticles

摘要

Hydrogen reduction treatments with variations in isothermal reduction temperature, duration, and partial pressure of hydrogen (P_H_2 ) are carried out on CeO_2 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 CeO_2 NPs is observed. Semiquantitative calculated concentrations of surface Ce~(3+) ions from x-ray photoelectron spectroscopy data demonstrate that ferromagnetism does not relate to the surface oxygen vacancies but to the surface Ce~(3+)/Ce~(4+) pairs. The higher the number of surface Ce~(3+)/Ce~(4+) pairs, the more robust the ferromagnetism appears.