EPR study of nanocrystalline CeO2 exhibiting ferromagnetism at room temperature

Electron paramagnetic resonance (EPR) spectroscopy complemented with X‐ray diffraction, X‐ray fluorescence, and optical spectroscopy was used to study nanocrystalline CeO2 powder samples that exhibit weak room‐temperature ferromagnetism. EPR lines assigned to the Ce3+ trigonal sites were found for the first time in cerium dioxide that contains a trace impurity of Mn2+. This finding indicates that manganese dopant facilitates the conversion of the oxidation state of Ce4+ to Ce3+ in nanocrystalline CeO2. Our results support the view that Ce3+/Ce4+ pairs along with defects on the surface of nanoparticles are responsible for the ferromagnetism in CeO2. The EPR study reveals that the charge‐transfer mechanism proposed recently is more suitable to explain the origin of room‐temperature ferromagnetism in CeO2 than the F+‐centers exchange interactions.