Synthesis and Characterization of Undoped and Doped (Mn, Cu, Co) ZnO Nanoparticles: An EPR Study

Abstract

Diluted Magnetic Semiconductors are obtained by introducing dilute amount of transition metal ions into semiconductors and they are subjected to their promising applications to spintronics. Zinc Oxide (ZnO) nanoparticles, which are used in large scale both in research and technology, belong to dilute magnetic semiconductors (DMS). In this study, structural, optical, and magnetic characterization of the synthesized undoped and Mn, Cu, and Co-doped (5 %) ZnO nanoparticles by Co-precipitation method were performed. Crystal sizes of the synthesized unannealed ZnO nanoparticles have been determined to be ~8 nm and ~90 nm by XRD and SEM analyses, respectively. AFM analysis is used for the determination of the surface topographies of the synthesized samples. From the results of UV-Vis studies, the absorbance peaks for the synthesized ZnO nanoparticles have been appeared at ~335 nm and the mean gap energy is calculated to be 3.47 eV. Electron Paramagnetic Resonance (EPR) spectroscopy is performed for the magnetic characterization of synthesized ZnO nanosamples dominantly and Vibrating Sample Magnetometry (VSM) was also used as a complementary technique. No EPR signal has been observed for undoped synthesized ZnO nanoparticles where six resolved EPR resonance lines, four resolved EPR resonance lines, and a broad, single unresolved EPR resonance line was recorded for 5 % doped synthesized ZnO:Mn, ZnO:Cu, and ZnO:Co nanoparticles, respectively. For UV-irradiated and annealed samples, some new EPR resonance lines have also been arised originating from the defects and oxygen damage centers involved in the crystal structure of ZnO. VSM results indicated that none of the synthesized ZnO nanoparticles were purely in ferromagnetic character at room temperature.