Modification of crystal anisotropy and enhancement of magnetic moment of Co-doped SnO(2) thin films annealed under magnetic field

Co-doped SnO(2) thin films were grown by sputtering technique on SiO(2)/Si(001) substrates at room temperature, and then, thermal treatments with and without an applied magnetic field (H(TT)) were performed in vacuum at 600°C for 20 min. H(TT) was applied parallel and perpendicular to the substrate surface. Magnetic M(H) measurements reveal the coexistence of a strong antiferromagnetic (AFM) signal and a ferromagnetic (FM) component. The AFM component has a Néel temperature higher than room temperature, the spin axis lies parallel to the substrate surface, and the highest magnetic moment m =7 μ(B)/Co at. is obtained when H(TT) is applied parallel to the substrate surface. Our results show an enhancement of FM moment per Co(+2) from 0.06 to 0.42 μ(B)/Co at. for the sample on which H(TT) was applied perpendicular to the surface. The FM order is attributed to the coupling of Co(+2) ions through electrons trapped at the site of oxygen vacancies, as described by the bound magnetic polaron model. Our results suggest that FM order is aligned along [101] direction of Co-doped SnO(2) nanocrystals, which is proposed to be the easy magnetization axis.