Defects Induced Ferromagnetism in Mg-doped ZnO Nanoparticles

Abstract

Zn1-xMgxO (x = 0, 5, 10, 15, 20) nanoparticles were successfully synthesized using sol-gel method. Structural analysis has been found to reveal that synthesized nanoparticles characterize wurtzite phase having hexagonal structure. Crystallite size calculated using Debye-Scherer equation has indicated a decrease in crystallite size from 20 to 11 nm. The peak shifting towards higher diffraction angle with increasing Mg-doping concentration has confirmed Mg-substitution. Morphological analysis has been found to reveal almost spherical morphology with average particle size 15 nm for 10% Mg-doped ZnO nanoparticles. Clear lattice fringes and sharp diffraction rings observed from HRTEM and SAED patterns, respectively, also revealed formation of well crystallized nanoparticles. EDS patterns has showed the successful doping of Mg in ZnO lattice without formation of any impurity phases. PL spectra revealed blue-shift in band gap with increasing Mg-doping concentration and the reason has been attributed to the wider band gap of MgO (7.3 eV) in comparison to ZnO (3.17 eV). The decreasing ESR signal with increasing Mg-doping concentration has clearly indicated the decreasing oxygen vacancy/defects. All the synthesized nanoparticles have been found to display room temperature ferromagnetism. Increasing Mg-doping concentration has resulted in decaying saturation magnetization value. The reason has been ascribed to decreasing oxygen vacancy/defects with increasing Mg-doping as revealed by ESR.