Enhancement of Virtual Magnetic Moment Formation in ZnO NPs by Li+ Ion Doping

Abstract

Lithium-doped ZnO (Zn1-xLixO) nanoparticles were fabricated using the hydrothermal process. XRD patterns showed that the Li+ ions substituted into different lattice sites depending on the level of the doping of Li+ into this semiconductor. The Williamson-Hall plots of the same XRD showed that the strains and sizes of the nanoparticles do not changed monotonically. Using the Tau plot to analyze the effects of the Li+ substitution on the optical (UV-Vis absorption) by the nanoparticles, the changes in the observed values of the energy gaps of the different doped semiconductor were seen not to decrease continuously. A VSM (vibrating sample magnetometer) was used to measure the hysteresis loops of our Zn1-xLixO NPs (originally, the nonmagnetic semiconductor XnO doped with the nonmagnetic Li+ ions). Our VSM measurements shows that the saturation magnetization (emu/g) and coercive force of these nanoparticles increased or decreased, respectively, as the level of Li+ doping increased. Photoluminescence emission at ≈ 510 nm showed that the Li+ doping led to the creation of more zinc vacancies, which in turn generates more virtual magnetic moments. Our results support the vacancy-induced d0 electron model of ferromagnetism in nonmagnetic ion-doped ZnO nanoparticles.