Structural, optical, vibrational, and magnetic properties of sol-gel derived Ni doped ZnO nanoparticles

Abstract

With a view to study structural, optical, vibrational, and magnetic properties of solgel derived Zn1−xNixO (x = 0.02, 0.04, and 0.06) nanoparticles, systematic investigations have been carried out. The Rietveld refinement of X-ray powder diffraction data revealed a single hexagonal phase with space group P63mc. The secondary phase of NiO appeared only in 6% Ni doped sample. Phonon modes in Ni doped ZnO nanoparticles were studied through Fourier transform infrared measurements. Furthermore, the enhancement in optical band gap with Ni doping from 3.29 to 3.32 eV has been observed through UV-visible spectroscopic analysis. Photoluminescence spectra of Zn1−xNixO show the UV-emission peak showing the blue shift with increase in doping concentration followed by broad visible (blue) emission corresponding to the defect emission whose intensity decreased with increasing Ni concentration. A clear room temperature ferromagnetism is observed in all samples but saturation magnetization decreased with increasing Ni content. The suitability of bound magnetic polarons (BMP) model is checked and numbers of BMPs are found to be of the order 1015 per cm3, which is very small for the percolation in ZnO. In the present case, oxygen rich stoichiometry with enhanced Zn-O bonding favours the indirect Ni-O-Ni ferromagnetic exchange coupling and reduction of oxygen vacancies leading to strong hybridization of Ni in ZnO host matrix responsible for room temperature ferromagnetism.