Ferromagnetism in co-doped zno particles prepared by vaporization-condensation in a solar image furnace

We report on the structural and magnetic properties of Co-doped ZnO particles prepared by vaporization-condensation in the solar furnace in Odeillo. X-ray diffraction data show no traces of Co segregation or any other phase different from ZnO. High-resolution electron microscopy (HREM) and transmision electron microscopy (TEM) techniques have also been used to characterize particles. Irrespective of their composition, the shape and size of the obtained particles, as well as their magnetic properties, clearly depend on the preparation conditions. The samples prepared in vacuum exhibit hysteretic behavior with low coercivity (about 100 Oe) at T = 5 K and saturation magnetization well below that expecte for Co2+ in a tetrahedral crystal field. On the other hand, samples prepared at high pressure (70-100 Torr inside the balloon) are paramagnetic. (c) 2004 Elsevier B.V. All rights reserved.