Unexpected magnetic properties in carbon-doped SnO2 from first-principles calculation

We employ spin-polarized density functional theory (DFT) calculations within generalized gradient approximation (GGA) to study the electronic structure and magnetic properties of C-doped SnO2 (SnO2:C) bulk and thin films. Our results indicate that a singly substitutional C (CO) does not induce magnetism, while the CO-CO pairs can unexpectedly activates short-range ferromagnetism in SnO2 bulk. The intrinsic defect O vacancy (VO) triggers local moment on the isolated CO atom but do not enhance the ferromagnetic (FM) coupling between CO atoms. When the substitutional CO atoms located at the surface of SnO2 thin films, system exhibits anti-ferromagnetic (AFM) feature, which is inconsistent with experimental observation. This diversity of magnetic behavior in SnO2:C system highlights the delicate interplay between electron correlations and localization. The magnetic properties are closely related to the intrinsic defect VO and the reduction of some Sn+4 ions to Sn+2 as a possible charge compensation mechanism.