Preparation characterization and magnetic properties of Zn sub((1-x))Co sub(x)O nanoparticle Dilute magnetic semiconductors

Abstract

Cobalt-doped ZnO nanoparticles having chemical formula Zn sub((1-x))Co sub(x)O (x=0.05, 0.10, 0.15, 0.20) were prepared by means of auto-combustion synthesis. Formation of monophasic wurtzite structure material was confirmed from XRD data. Inclusion of the Co sup(2+) ions in the ZnO matrix produced several fascinating effects in the structural, physical and magnetic properties of the nanoparticles. The lattice constants 'a' and 'c' got inflated and the average crystallite size shriveled from 25 nm to 17 nm with the increase of Co concentration 'x' in the sample. The FT-IR spectra showed the characteristic absorption bands in the range of 400cm sup(-1) to 576cm sup(-1) due to formation of Zn-O and Co-O stretching bonds in the samples. Scanning Electron Microscope (SEM) images show agglomerates of particles that are spherical in nature. Energy dispersive spectroscopy (EDS) spectra of the samples giving molecular weight percentages of the elements Zn, Co and O in the samples are in agreement with the calculated percentages within the limit of permissible error. Hysteresis, FC, and ZFC measurements made on the samples, exhibit presence of ferromagnetic phase in the materials. Energy band gap estimates made with the help of UV spectroscopy indicated a decreasing trend of band gap with increasing 'x' in the sample. Photoluminescence studies carried out with excitation wavelength of 318 nm gave several emission peaks ranging from green to violet emissions. This observation confirms the presence of vacancies (defects) in the nanoparticle samples. Luminescence decay time recorded was in the range microseconds for all the samples.