D⁰ Ferromagnetism Of Zn_1-xLa_xO Nanoparticles

Several types of "d0" oxide magnetic semiconductor were reported recently, including undoped and doped with d0 metal or lighter elements (such as C, N, P) oxide semiconductor. It is agreed with that defects are closely related to the ferromagnetic, according to the results of experiment and theoretical calculation. But which defects play the important role is still controversial.La-doped ZnO nanoparticles were prepared using hydrothermal method and sol-gel method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron Spectroscopy (XPS) and Raman spectrometer were utilized to observe the microstructure, the chemical states and the compositional elements in Zn1-xLaxO nanoparticles. The results indicate that La is doped into ZnO lattice and there is no La3+ ions cluster in ZnO nanoparticles.Magnetization curves as a function of applied magnetic field (M-H) at room temperature and the zero-field-cooled (ZFC) and field-cooled (FC) magnetization curve show that all samples are ferromagnetic at room temperature and the ferromagnetism of samples is intrinsic and free from ferromagnetic contamination. After annealing in the different atmosphere, the concentration of the intrinsic defects for sample was changed. The role of intrinsic defects in ferromagnetism of the sample was studied. Doping of La induces increasing of oxygen vacancies and eliminating of Zn vacancies. Oxygen vacancies enhance the magnetism of the sample. The zinc vacancies weaken magnetism of the sample. In other words, exchange mechanisms associated with oxygen vacancies and zinc vacancies are responsible for ferromagnetism in the Zni-xLaxO nanoparticles.