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Cerium dioxide is a wide gap semiconductor with uorite structure widely used for catalysts. It has recently been proposed as a diluted magnetic semiconductor (SMD) for spintronic applications by slightly doping it with magnetic ions such as Co, Fe, Mn, etc. In this work we investigate the role of oxygen vacancies in the parent, undoped compound CeO2 by electron spin resonance (EPR) and magnetization experiments. Pure CeO2 powders were synthesized by the liquidmix method using 99.99% Ce(NO3):6H2O. The samples were calcined in air at 600 C. The X-ray diffraction analysis indicates a uorite structure with no secondary phases. The CeO2 powders so obtained were subsequently annealed at 500 C in an low oxygen content atmosphere, under a pressure of 2 10 ..2 mbar. These treatments were applied for 5 hs, 10 hs, 15 hs, and 20 hs with the aim of introducing an increasing amount of oxygen vacancies in a controlled way. Magnetization vs. eld measurements were performed in a QD Versalab VSM showing an increase of the magnetic signal for samples annealed at low oxygen pressures. The EPR experiments were done at room temperature in a Bruker ESP-300 spectrometer using a microwave frequency of 9.7 GHz (X-band). In all the cases, the annealed samples revealed an EPR spectrum consisting of a single line close to g = 2. Interestingly, we observed that the intensity of the EPR signal increases almost linearly with increasing annealing time. In other words, the number of paramagnetic centers that are at the origin of the EPR absorption is directly correlated with the number of oxygen vacancies. We compare the EPR and magnetization results, and discuss them in terms of Ce 3+ and oxygen vacancies contents and the nature of the magnetic interactions present in the compound.

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