Identifying the sources of ferromagnetism in sol-gel synthesized Zn1-xCoxO (0 ≤ x ≤ 0.10) nanoparticles

We have carefully investigated the structural, optical and electronic properties and related them with changes in the magnetism of sol-gel synthesized Zn1-xCoxO (0 <= x <= 0.10) nanoparticles. Samples with x < 0.05 were free of spurious phases. Samples with x < 0.03 were found to be with only high spin Co2+ ions into ZnO structure, whereas sample with x=0.05, exhibited the presence of high spin Co2+ and low spin Co3+. We found that the intensity of the main EPR peak associated with Co2+ varies with the nominal Co content in a similar manner as the saturation magnetization and coercive field do. These results point out that the ferromagnetism in these samples should directly be correlated with the presence of divalent cobalt ions. Bound magnetic polaron (BMP) model and the charge transfer model are insufficient to explain the ferromagnetic properties of Zn1-xCoxO nanoparticles. The room temperature ferromagnetism (RTFM) may be originated from a combination of several factors such as the interaction of high spin Co2+ ions, perturbation/alteration and/or changes in the electronic structure of ZnO close to the valence band edge and grain boundary effects. (C) 2016 Elsevier Inc. All rights reserved.