Correlation between structural, electrical, dielectric and magnetic properties of semiconducting Co doped and (Co, Li) co-doped ZnO nanoparticles for spintronics applications

A series of co-doped Zn0.96-yCo0.04LiyO(0.00 ≤ y ≤ 0.10) nanoparticles has been synthesized by sol-gel technique. The quantity of each constituent calculated from Rutherford backscattering spectrometry (RBS) and electron energy loss spectroscopy (EELS) has been found to be in close agreement with the nominal compositions. The presence of single phase hexagonal crystalline structure has been confirmed by refinement fitting rietveld analysis of X-ray diffraction (XRD) data and high resolution transmission electron microscope (HRTEM) measurements. Elemental mapping confirmed the homogeneous distribution of Li in the ZnO:Co matrix using energy filtered TEM mode. Room temperature dc-resistivity were measured 1200 × 104 ·cm for ZnO:Co while in co-doped nanoparticles the values decreased to a range 3-7 × 104 ·cm due to additions of hole carriers. The p-type carriers with concentration ranging 2.9 × 1018 to 9.8 × 1018/cm3 are found using Hall measurements. From the imaginary part of dielectric measurement, we found that Tc varies in a wide range of 455-510 K. The saturation magnetization at 50 K lies in the range 0.18emu/g to 0.45emu/g for different Li concentrations. We observed a non-monotonic dependence of hole carriers, DC resistivity, dielectric transition temperature and magnetic moment on varying Li contents. We may argue that hole carrier concentration is responsible for stabilizing and promoting magnetism in co-doped (Co, Li) ZnO semiconductors for data storage and spintronics devices.