Magnetic Resonance Study of Co-doped ZnO Nanomaterials: a Case of High Doping

摘要

Magnetic resonance could be very useful technique in clarification of many unresolved problems in nano-magnetism of ZnO doped with transition metal ions, in particular with Co. In the first part of this paper a review of investigations of ZnO:Co nanomaterials using magnetic resonance techniques - electron paramagnetic resonance (EPR) and ferromagnetic resonance (FMR) - is presented. The preparation methods, the structural characteristics of the obtained materials and the main results of EPR/FMR studies are briefly described. In the second part the EPR/FMR investigations of a new series of (CoO)_n(ZnO)_1-n nanocomposites (where the composition index n = 0.4, 0.5, 0.6 and 0.7) prepared by the hydrothermal synthesis have been presented. XRD measurements displayed peaks from ZnO and ZnCo₂O₄ phases as well as weak lines attributed to Co(OH)₂ phase. The temperature and Co concentration dependence of the calculated EPR/FMR parameters (resonance fields, linewidths, integrated intensities) were studied. Three main components were recognized - a broad line attributed to nanoparticles of ZnCo₂O₄ phase, two narrow lines arising from Co²⁺ ions in ZnO nanoparticles, and a narrow component probably from the impurity Co₃O₄ phase.