Abstract: Co doped CeO 2 nanocrystals with different Co concentrations were prepared by hydrothermal method .The crystal structure , microscopic morphology and magnetic properties of these nanocrystals were investigated by XRD, Raman, SEM and PPMS.The results of XRD and Raman indicate that the CeO2 nanocrystals with different Co concentrations are cubic fluorite structure .No Co and Co oxides peaks were found, which indicates that Co doping replaced the Ce in CeO 2 lattice.The characteristic peaks of XRD show no obvious translation , so the lattice distortion of CeO 2 is not obvious due to Co doping .SEM images show that the nanocrystals are octahedrites with an edge length of about 600-800 nm.Microscopic morphology of Co doped CeO 2 nanocrystals has obvious relationship with the Co doping concentration . With the increase of Co doping concentration , the edge of octahedrites become from clear to fuzzy , and the surface from smooth to rough .PPMS measurements show that all the samples exhibit room temperature ferromagnetism .With the increase of Co doping concentration , the saturation magnetization increases first and then decreases , and the 5;Co doped CeO 2 nanocrystals has the maximum saturation magnetization .The magnetic properties of nanocrystals are obviously changed by different Co doping concentration .The room temperature ferromagnetism of nanocrystals can be modulated by changing the concentration of Co .

Key words: Co doped CeO 2 nanocrystals with different Co concentrations were prepared by hydrothermal method .The crystal structure , microscopic morphology and magnetic properties of these nanocrystals were investigated by XRD, Raman, SEM and PPMS.The results of XRD and Raman indicate that the CeO2 nanocrystals with different Co concentrations are cubic fluorite structure .No Co and Co oxides peaks were found, which indicates that Co doping replaced the Ce in CeO 2 lattice.The characteristic peaks of XRD show no obvious translation , so the lattice distortion of CeO 2 is not obvious due to Co doping .SEM images show that the nanocrystals are octahedrites with an edge length of about 600-800 nm.Microscopic morphology of Co doped CeO 2 nanocrystals has obvious relationship with the Co doping concentration . With the increase of Co doping concentration , the edge of octahedrites become from clear to fuzzy , and the surface from smooth to rough .PPMS measurements show that all the samples exhibit room temperature ferromagnetism .With the increase of Co doping concentration , the saturation magnetization increases first and then decreases , and the 5;Co doped CeO 2 nanocrystals has the maximum saturation magnetization .The magnetic properties of nanocrystals are obviously changed by different Co doping concentration .The room temperature ferromagnetism of nanocrystals can be modulated by changing the concentration of Co .