Effects of oxygen vacancies on the room-temperature ferromagnetism of Co-doped polycrystalline CeO2

Pure and Co-doped single-phase CeO2 crystals were synthesized by a solid-state reaction method. Samples of different oxygen vacancy concentration were studied, including (1) as-sintered crystals, (2) powders ground from the same crystal, and (3) a cold-pressed pellet from the ground powder that was unannealed and annealed at 800 °C. By analyzing the magnetic behaviors, surface/volume ratio and O vacancy concentration, the effects of oxygen vacancies on the room-temperature ferromagnetism (RT-FM) of Co-doped CeO2 were systematically investigated. The results confirm that the RT-FM observed in Co-doped CeO2 has a direct relationship with the oxygen vacancy concentration, and support the oxygen vacancy mediated FM mechanism.