The structural, optical properties and the origin of spin functionality in the Co modified TiO2 nanoparticles

Abstract We attempt to investigate the structural, optical and magnetic properties of Cobalt (Co) modified TiO2 nanoparticles. The polycrystalline TiO2: Co (1%, 3%, 5% and 7%) powders were produced by using the hydrothermal synthesis route. The anatase phase of the synthesized powder samples was confirmed from the X-ray diffraction patterns and the crystalline structure was analyzed by employing the Rietveld refinement method. Significant variation in the unit cell parameters (a = b = 3.781; c = 9.499 for 1% Co concentration and a = b = 3.779; c = 9.504 for 7% Co concentration) was observed upon the partial substitution of the Co in place of Titanium (Ti). In addition, the Raman spectra of the doped compounds was found to be blue shifted. The optical band gap decreased from 3.18 eV for parent compound to 1.91 eV for 7% Co content in TiO2. Ferromagnetic ordering was emerged with the Co doping and the field dependent magnetization measurement revealed local competition between the ferromagnetic and a paramagnetic state against the doping concentration. Our findings advise that the ferromagnetic coupling definitely emerged in TiO2 upon the controlled substitution of Co.