Ni-doped SnO2 nanoparticles: Structural insights and magnetic behavior via X-ray absorption spectroscopy

Abstract

This study investigates the effect of Ni dopant on the electronic structure and magnetic properties of SnO₂ nanoparticles. By employing Sn and Ni-K edge X-ray absorption spectroscopy (XAS), we examined the variations in the local structure induced by Ni doping. Our results demonstrate that when Ni atoms replace Sn, it results in the creation of numerous oxygen vacancies (O_v). Similar spectral behavior of the samples, with respect to SnO₂, in Sn-K edge X-ray Absorption Near Edge Structure (XANES) indicates successful incorporation of Ni ions into SnO₂ lattice without causing structural deformation. The position of the white-line in the Ni-K edge XANES confirms the absence of Ni clusters or NiO, indicating the observed Room-Temperature Ferromagnetism (RTFM) is not due to magnetic Ni species. Extended X-ray absorption Fine Structure (EXAFS) analysis shows changes in coordination numbers (CN) post-doping, suggesting emergence of O_v, while the similarity in bond-lengths (R) confirms the substitution of Sn by Ni atoms in the SnO₂ matrix. Moreover, the weak ferromagnetism (FM) observed in the undoped sample indicates intrinsic defects within the sample, whereas the enhanced RTFM in Ni-doped sample is attributed to a synergistic effect of both O_v and the dopant atoms. This can be explained by the formation of Bound Magnetic Polarons (BMP). A good fit to the spin wave model in the higher temperature range (150–300 K) further supports the role of Ni doping in the observed RTFM.