Origin of ferromagnetism in Zn-doped SnO2 from first-principles study

Density-functional calculations are carried out to study the magnetic properties and electronic structures of Zinc-doped SnO2 systems with and without oxygen (tin) vacancies. The magnetic moment increases almost linearly with the increase of impurity concentration (from 4% to 25%) in the cases without oxygen and tin vacancies. The induced magnetic moments mainly come from the first shell oxygen atoms surrounding the doped Zn atom. The magnetic moments become smaller (larger) when oxygen (tin) vacancy is introduced, which is not as seen in Co and Ni doped SnO2 systems. Oxygen (tin) vacancy defects are easily formed at the nearest distance from the doped Zn atom and the largest possible magnetic moments will appear at the concentration of Zn atom between 6.25% and 12.5%. The calculated results also show that Zn–Zn are ferromagnetically coupled, and how the magnetic moments vary with Zn–Zn distance when only two Zn atoms were doped into a SnO2 supercell. However, Zn–Zn show anti-ferromagnetic coupling when three Zn atoms are doped in the same SnO2 supercell. The results may be helpful for further study on TMs doped SnO2 systems.