Synthesis, structural, morphological, optical and magnetic properties of Zn1−xCoxO (0 ≤ x ≤ 0.36) nanoparticles synthesized by sol-gel auto combustion method

Abstract

Nanoparticles of Zn1−xCoxO (0 ≤ x ≤ 0.36) were successfully synthesized by sol-gel auto combustion method. Influence of Co2+ doping on structural, morphological, optical and magnetic properties has been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR), UV–visible absorption spectroscopy, vibrating sample magnetometer (VSM) and Superconducting quantum interference device (SQUID). The X-ray diffraction analysis reveals that the formation of single phase having hexagonal wurtzite structure along with secondary phase (Co3O4). The lattice parameters, Crystallite sizes, volume of the unit cell, X-ray density and bond length of pure and Co2+ doped ZnO nanoparticles were determined from XRD analysis. SEM analysis showed that the prepared nanoparticles are in the nano regime, nearly spherical and loosely agglomerated. EDAX analysis showed that composition obtained is near stoichiometric. The presence of functional groups and the chemical bonding due to Co2+ doping is confirmed by FTIR spectra. UV–visible absorption spectra showed that absorption edge to shift towards the higher wavelength with increasing Co2+ concentration while the corresponding energy band gap of semiconductor nanoparticles decreases with increasing Co2+ concentration. From VSM and SQUID analysis, pure and Co2+ doped ZnO nanoparticles show diamagnetic and paramagnetic behaviour at room temperature respectively. The significant changes in M–H loop of diamagnetic behaviour to paramagnetic behaviour are due to non-availability of free carrier concentration for long range ferromagnetic interaction with our system.