Improved magnetic properties of CeO2 nanoparticles on Ce3+valence states by Fe3+/Co2+/Mn2+-doped CeO2 nanoparticles

Undoped CeO2 nanoparticles and CeO2 nanoparticles doped with 20% Fe3+, Co2+ or Mn2+ synthesized using a co-precipitation method and calcined at 600 degrees C were studied. All synthesized samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray absorption near edge spectroscopy (XANES), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM). The XRD spectra exhibited peaks corresponding to a single phase face-centered cubic CeO2 in all samples. Crystallite sizes decreased to 10.5 +/- 0.3 nm for the Mn2+ dopant compared to that of undoped CeO2 for 15.0 +/- 0.8 nm. The presence of Ce3+, Ce4+, Fe3+, Co2+, Mn2+ ions and oxygen vacancies in all samples containing CeO2 was determined from the XANES and XPS spectra. Magnetic results obtained from undoped CeO2 exhibited ferromagnetic (FM) behavior at room temperature (RT) with a magnetization (M) of 0.005 emu/g that can be explained in terms of Ce3+ and an oxygen vacancy mediated F-center exchange (FCE) mechanism. Doped CeO2 samples exhibited higher M values compared to that of undoped CeO2, especially in Fe3+-doped CeO2 samples, which showed the highest M value, 0.09 emu/g. The roles of Ce3+ and their spin electrons are discussed. The novelty of this work is the formation of a single phase CeO2 nanoparticles with high doping concentration of 20% and all shows ferromagnetism above RT. As a result, this research may open up new avenues for the design of advanced spintronic devices.