Enhanced room-temperature ferromagnetism on Co-doped CeO₂ nanoparticles: Mechanism and electronic and optical properties

The present study reports the effect of Co doping on the structural, optical, magnetic, and electronic properties of CeO₂ nanoparticles (NPs) synthesized by a simple low-temperature co-precipitation method. Co doping was introduced by adding CoCl₃ with different mole percentages (0%, 2%, 4%, and 6%) to cerium nitrate, which resulted in room-temperature ferromagnetism (RTFM). TEM and XRD analysis showed that the Co-doped CeO₂ NPs are monodispersed with face centered cubic structure. The 6% Co-doped CeO₂ NPs showed a coercivity value of 155 Oe and saturation magnetization of 0.028 emu/g at room temperature. The electronic structures of the as-prepared CeO₂ and Co-doped CeO₂ NPs were investigated by X-ray absorption near-edge structure (XANES) spectroscopy. The XANES spectra at Ce M- and L-edges clearly indicated a decrease in the valency state of Ce ions from Ce⁴⁺ to Ce³⁺ upon Co doping. This causes redistribution of oxygen ions and Co-Co bonding. The XANES study revealed that Co doping plays a prominent role in improving the ferromagnetism, as Co replaces the Ce site in the CeO₂ cubic lattice and the concentration of oxygen vacancies may not be high enough to form a delocalized impurity band for enhancing the magnetic percolation of Co-doped samples. The XANES spectra at Co L-edges indicate direct Co-Co bond formation in the CeO₂ lattices and also a weak bond with O ions. This is in agreement with the magnetic measurements which indicate that Co atoms induce enhancement in magnetic behavior in CeO₂ nanostructures. (Graph Presented).