Oxygen-vacancy-induced ferromagnetism in undoped SnO2 thin films

G. S. Chang,
J. Forrest,
E. Z. Kurmaev,
A. N. Morozovska,
J. A. McLeod,
A. Moewes,
T. P. Surkova,
Nguyen Hoa Hong

Інститут проблем матеріалознавства ім. І. М. Францевича НАН України , вул. Кржижановського 3, Київ, 03142, Україна
Physical Review B - Maryland, USA: Американське Фізичне Суспільство (APS), 2012, #85


We investigated the possible formation and segregation of oxygen vacancies near the surface of SnO2 thin films from oxygen K-edge x-ray emission and absorption spectra and found that the distribution of O 2p unoccupied states for ferromagnetic SnO2 thin films is different from that of postannealed SnO2 films under oxygen atmosphere showing diamagnetic behavior. This spectroscopic result suggests that oxygen vacancies can be the source of the surface-induced magnetism in SnO2 thin films. This possibility was then explored by calculating the lowest energy levels of the structural defects (impurities or neutral vacancies) with two localized carriers near the surface of SnO2 film using a quantum-mechanical approach combined with the image charge method. A magnetic triplet state is found to be the ground state of those defects in the vicinity of the SnO2 surface, whereas the nonmagnetic singlet is the ground state of bulk SnO2. Surface-induced ferromagnetic order can appear at room temperature via 2D magnetic percolation once the vacancy concentration is greater than 3*1016 m-2.