Structural analysis and magnetic properties of cobalt-doped nanotitania

Abstract

The study is an attempt to bridge the gap between experimental observations and the theoretical predictions on cobalt (Co) doped TiO2 nanoparticles prepared by low cost sol-gel method. Single phase anatase TiO2 nanocrystals with particle size ranging between 16 and 32 nm observed minor distortions in TiO2 unit cell, after cobalt substitution (3 and 5 at.%), due to its larger ionic radius, which leads to creation of oxygen vacancies. Doped TiO2 showed significant diminution from 3.51 to 3.25 eV in the band gap, supported by density functional theory. Presence of nonlinear magnetization within lower field region was also observed which indicate the existence of weak ferromagnetism dominated by paramagnetic behaviour at high field region, suggesting a mixed magnetic phase. Magnetic observations are well supported with bound magnetic polaron (BMP) model. The observed band gap shrinkage and magnetic behaviour both are associated to the oxygen vacancies created by Co doping.