Oxygen vacancies driven size-dependent d0 room temperature ferromagnetism in well-dispersed dopant-free ZnO nanoparticles and density functional theory calculation

This paper reports the intrinsic size-dependent d(0) room-temperature ferromagnetism in dopant-free ZnO nanoparticles, which were fabricated by thermal decomposition route. The size of ZnO nanoparticles can be controlled by simply tuning the amount ratio of solvent. Transmission electron microscope shows that the ZnO nanoparticles are well-dispersed without aggregation. Magnetic measurement suggests that the undoped ZnO nanoparticles show room temperature ferromagnetic characteristic, which is sensitive with the particle size. Photoluminescence spectra and X-ray photoelectron spectroscopy measurements elucidate that the relative concentration of oxygen vacancies increase as the particle sizes decrease, leading to long-range ferromagnetic ordering in the undoped ZnO nanoparticles. A correlation among the particle size, ferromagnetism and relative concentration of oxygen vacancies is established, which demonstrates that oxygen vacancies play a key role to induce ferromagnetic ordering. Furthermore, density functional theory calculation demonstrates that the oxygen vacancies in ZnO with positive charge trapping can induce polar-magnetization which is stable states. The correlation between experiments and simulations suggests that the ferromagnetic behavior in diluted magnetic semiconductors can be conveniently manipulated by tuning the surface-volume ratio of nanostructures and surface defects, which is of great significance to understand and explore novel diluted magnetic semiconductors. (C) 2017 Elsevier B.V. All rights reserved.