Surface defect mediated magnetic interactions and ferromagnetism in Cr/Co Co-doped ZnO nanoparticles

We report the structural and ferromagnetic properties of Zn0.97-xCrxCo0.03O (x=0.0, 0.03, 0.06 and 0.09) nanoparticles (NPs) synthesized through citric-gel route. X-ray diffraction (XRD) and selected area electron diffraction (SAED) results show the single phase nature with hexagonal wurtzite structure, and reveal the incorporation of Cr3+ and Co2+ ions into lattice positions of Zn2+ ions in ZnO lattice. The average size of NPs decreases from similar to 24 to 9 nm with increasing Cr dopant concentrations (x). Micro-Raman and X-ray photoelectron spectroscopy (XPS) studies show the presence of oxygen vacancies (V-o) defects. The XPS study shows interaction between Cr-Co dopant and transfer of electrons from Cr (3d) state to unfilled (3d) state of Co. The observed ferromagnetism is intrinsic in nature, and not due to any metallic segregation or impurity phase. The oxygen vacancies mediated the dopant ions interaction, and the ferromagnetism can be elucidated by bound magnetic polaron (BMP) mechanism. (C) 2012 Elsevier B.V. All rights reserved.