Room temperature ferromagnetism in Zn0.99La0.01O and pure ZnO nanoparticles

• La-doped and pure ZnO nanoparticles were synthesized by sol–gel method.
• Room temperature ferromagnetism (RTFM) was found in both La-doped and pure ZnO nanoparticles.
• RTFM related to oxygen vacancies enhanced by La doping is d0 ferromagnetism.

Room temperature ferromagnetism (RTFM) was observed in both La-doped and pure ZnO nanoparticles synthesized by the sol–gel method. RTFM is intrinsic according to the results of X-ray diffraction and X-ray photoelectron spectroscopy. The saturation magnetization (MS), the remnant magnetization at zero field and coercive field are 5 × 10−3, 7 × 10−4 emu g−1, 100 Oe for Zn0.99La0.01O nanoparticles and 1.5 × 10−4, 1 × 10−5 emu g−1, 50 Oe for pure ZnO nanoparticles, respectively. The magnetization is enhanced greatly by doping of La. Furthermore, the MS of Zn0.99La0.01O nanoparticles decreases from 0.005 to 0.001 emu g−1 as the annealing temperature increases from 500 to 700 °C. The doping of La introduces more oxygen vacancies into ZnO. The decrease of annealing temperature also produces more oxygen vacancies in La-doped ZnO. These results indicate that the origin of the RTFM is related to oxygen vacancies.