Consequences of (Cr/Co) co-doping on the microstructure, optical and magnetic properties of microwave assisted sol-gel derived TiO2 nanoparticles

In the present work, codoped nanoparticles (NPs) of chemical formula Ti1-xCrx/2O2 (x = 0, 0.04 and 0.06) were synthesized by microwave assisted sol-gel method and characterized for their microstructural, compositional and magnetic properties. Rietveld refinement of the x-ray diffraction data and Raman spectroscopy confirm the single phase nature of all the compositions with anatase tetragonal structure. TEM images reveal the variation in the shape and size of the particles with the increase in Cr/Co doping. Fourier transform infrared (FTIR) spectra described the different stretching and vibrational modes related to the functional groups that exist in the samples. Raman and x-ray photoelectron spectroscopy (XPS) establish highly pure, appropriate stoichiometric nature and oxidation state of the compositions. A red shift in the UV-visible absorbance spectra is observed for the codoped samples that signify the bandgap narrowing (i.e. from 3.04 to 2.92 eV) attributed to the formation of defects in the host lattice. Analysis of photoluminescence spectra shows that the dopant ions alter the oxygen vacancies that directly influence the electron hole recombination rate. The magnetic hysteresis loops of 2% and 3% Cr/Co doped samples exhibit room temperature ferromagnetic (RTFM) nature. The value of saturation magnetization enhances with the increase of Cr/Co concentration. These results strongly suggest that the oxygen vacancies play a pivotal role to induce ferromagnetism at room temperature in oxide semiconductors and these oxides are potential candidate for spintronics device applications.