Regulation of magnetism on Fe- and Ni-doped SnO2 (1 1 0) surfaces by oxygen vacancy and adsorbed O2 molecule

We investigated the ferromagnetism of Fe- and Ni-doped SnO2 (1 1 0) surfaces and the regulation of the ferromagnetism on doped surfaces by the oxygen vacancy and adsorbed O2 molecule. The introduction of Fe/Ni dopant can make the nonmagnetic SnO2 (1 1 0) surface have a magnetic moment of 3.45 µB/1.97 µB and exhibit stable ferromagnetic coupling. After forming oxygen vacancy under oxygen-deficient conditions, a fraction of the remaining electrons provided by vacancy is acquired by the doped atom, which reduces the number of unpaired electrons in the doped atom d shell, thereby reducing the surface magnetic moment by about 0.6 µB. The oxygen vacancy reduces the magnetization of the bound magnetopolaron, which leads to the weakening of the surface ferromagnetic coupling. The free O2 molecule can exothermically adsorb on the defect surface and fill the oxygen vacancy, forming a magnetic cluster with the doped atom. Although the magnetic moment of the spontaneously adsorbed O2 molecule decreases due to obtaining a small number of electrons from the surface, the magnetic moment of the O2-adsorbed surface increases about 1.0 µB. The magnetic coupling of the O2-adsorbed surface is determined by the competition mechanism of antimagnetic coupling between O2 molecules and ferromagnetic coupling between magnetopolarons.