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The present study reports the effect of Co doping on the structural, optical, magnetic, and electronic properties of CeO 2 nanoparticles (NPs) synthesized by a simple low-temperature co-precipitation method. Co doping was introduced by adding CoCl 3 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 CeO 2 NPs are monodispersed with face centered cubic structure. The 6% Co-doped CeO 2 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 CeO 2 and Codoped CeO 2 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 Ce 4+ to Ce 3+ 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 CeO 2 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 CeO 2 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 CeO 2 nanostructures.

The manifestation of substitution and dimension induced modifications in the magnetic origin and photocatalytic properties of Dy substituted bismuth ferrite (BDFOx) particulate and fiber nanostructures are reported herein. A gradual transformation from rhombohedral to orthorhombic structure is observed in BFO with the increasing concentration of Dy. Substitution induced size reduction in particulate and fiber nanostructures is evident from the scanning and transmission electron micrographs. Energy band structures of both particulate and fiber nanostructures are considerably influenced by the Dy substitution, which is ascribed to the formation of new energy states underneath the conduction band of host BFO. Field dependent and temperature dependent magnetic studies reveal that the origin of magnetism in pure BFO systems is due to the antiferromagnetic-core/ferromagnetic-shell like structure. On the other hand, it gets completely switched into 'canted' spin structures due to the substitution induced suppression of cycloidal spins in BFO, which is found to be the origin of magnetism in BDFOx particulate and fiber nanostructures. The visible light driven photocatalytic activity of BDFOx nanostructures is found to be enhanced with increasing concentration of Dy. Substitution induced band gap modification, semiconductor band bending phenomenon mediated charge transfer and reduced recombination resistances are attributed to the observed photocatalytic enhancements in these nanostructures.