Effect of doping and annealing on the electronic structure and magnetic properties of nanoscale Co and Zn co-doped SnO2: An experimental study and first-principles modeling

Abstract

The influence of Co and Zn co-doping and annealing on the structure and magnetic properties of SnO2 nanoparticles were investigated in relation to electronic structure. The powder X-ray diffraction patterns revealed single phase tetragonal rutile structure for both as-synthesized and annealed Co and Zn co-doped SnO2 samples. The results of XPS and first-principles modeling emphasized that both the co-doped metals incorporated to SnO2 host lattice with an oxidation state of 2 + inducing the formation of oxygen vacancies under cation substitution of tetravalent Sn. Moreover, XPS spectra showed the O/(Sn + Co + Zn) ratio which has been strongly reduced under annealing for creating additional oxygen vacancies. Field dependent magnetization studies demonstrated the existence of room temperature ferromagnetism (RTFM) for the as-synthesized co-doped (Co, Zn: SnO2) and all the annealed samples. The origin of observed RTFM was correlated to the oxygen vacancies. The results of first-principles modeling demonstrated that the increase in the concentration of Co/Zn dopant offers not just an increase of total magnetic moment of the system but also control the magnetic interactions between magnetic moments on metal ions and oxygen atoms. The combination of experimental and theoretical techniques unveiled a correlation between observed RTFM and dopant atom interactions within a host lattice. Our findings provide new insight into the interaction of transition metals (Co/Zn) within co-doped systems and new evidence for the oxygen vacancy-mediated room temperature ferromagnetism.