O.M. Lemine

Sol–gel synthesis, structural, optical and magnetic properties of Co-doped ZnO nanoparticles

Abstract We report the synthesis of Zn1−xCoxO nanoparticles prepared by a sol–gel processing technique for x ranging from 0 to 0.05. The structural, morphological, optical and magnetic properties of the as-prepared nanoparticles were investigated by XRD, XPS, transmission electron microscopy, UV measurements, photoluminescence and superconducting quantum interference device. The structural properties showed that the obtained nanoparticles are single phase wurtzite structure and no secondary phases were detected which indicated that Co ions substituted for Zn ions. The energy gap decreased gradually with increasing doping concentration of Co. The photoluminescence spectra show a shift of the position of the ultraviolet emission to long wavelength and the intensity decreases with increasing Co. The Magnetic measurements at room temperature reveal diamagnetic behavior for sample with lower concentration and the presence of both paramagnetic and ferromagnetic behavior for increasing concentration.

Induced ferromagnetism in mechanically milled nanocrystalline In2O3 powder

In this work, we have investigated structural, optical and magnetic properties of In2O3 powder samples prepared by mechanical milling process at different milling times. These samples have evidenced a ferromagnetism order at room temperature. The optical and magnetic properties were explained by the increase of quantum confinement, defects and strain effects after mechanical milling. Introduction Undoped semiconductor oxides are well known as diamagnetic materials. However, recent studies have revealed that oxides nanostructures such as nanowires and nanoparticles can exhibit ferromagnetic order. The ferromagnetism is usually associated to the increase of defects such as oxygen vacancies, quantum confinement and etc. However, further studies are necessary in order to understand the nature of magnetic properties in undoped oxides. In this work, we have investigated structural, optical and magnetic properties of In2O3 nanoparticles (NP) prepared by mechanical milling at different milling times. We have measured X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman Spectroscopy, Photoluminescence (PL) and magnetic properties of In2O3 nanoparticles. Methods and Results Commercial undoped In2O3 powder (purity: 99.9%) has been milled under air in a planetary ball mill for different milling times. Zirconia grinding medium has been used in order to avoid any contamination with magnetic impurities. The samples were investigated using different experimental techniques such as XRD, SEM, Raman and Photoluminescence. XRD measurements were performed using a Rigaku powder diffractometer and the morphology of samples was investigated by a Field Emission Gun Scanning Electron Microscopy (FEG-SEM). The Raman and PL measurements were performed in a 0.5m Andor spectrometer coupled with a Si CCD. The magnetic characterization was performed using SQUID VSM magnetometer. The XRD data have evidenced the bcc-phase, reduction of crystallite size and changes of microstrain for all In2O3 nanoparticles. Figure 1 shows typical magnetic results obtained for the sample after 48h milling time. It was observed that after mechanical milling process the samples present ferromagnetic order. Figure 2 shows typical optical results for the same sample. The PL spectra have showed a visible band related to oxygen vacancy transition. It was observed that this band presents a blue shift with increasing milling times. The Raman spectra showed several peaks related to the cubic phase of In2O3 nanoparticles. It was also observed that for higher milling times such as 96h, additional Raman peaks were revealed due to the change of cubic crystal phase to hexagonal phase. DOI: 10.17648/bwsp-2017-70026 18th Brazilian Workshop on Semiconductor Physics (BWSP 2017) 18th Brazilian Workshop on Semiconductor Physics (BWSP 2017) -60 -40 -20 0 20 40 60 -8 -6 -4 -2 0 2 4 6 8 -0,04 0,00 0,04 -0,010 -0,005 0,000 0,005 0,010 (b) 300 K 0 h M a g n e ti z a ti o n ( 1 0 -2 e m u /g )