High-temperature ferromagnetism in Co-doped CeO2 synthesized by the coprecipitation technique

The aim of the present study is to check the influence of annealing under vacuum and a mixture of N-2-H-2 atmosphere on the magnetic properties of polycrystalline Co-doped CeO2 diluted magnetic oxides (DMOs) with Co concentrations of 5 at% synthesized using the coprecipitation technique. X-Ray diffraction (XRD) patterns and transmission electron microscopy (TEM) showed for all samples the expected CeO2 cubic fluorite-type structure and that Co ions are uniformly distributed inside the samples. Room-temperature Raman and photoluminescence (PL) spectroscopies indicate an increase in the concentration of oxygen vacancies upon Co doping and further annealing. Field dependent magnetization measurements revealed a paramagnetic behavior for as-prepared Co-doped CeO2, while a ferromagnetic behavior appears when the same samples are annealed under vacuum or N-2-H-2 atmosphere. Temperature dependent magnetization measurements suggest that the observed ferromagnetism is due to the presence of metallic Co clusters with nanometric size and broad size distribution. These results are supported by electron paramagnetic resonance studies.