Effects of Buffer Layer on Structure and Ferromagnetism of Co-Doped SnO$_{2}$ Films

The thickness of SnO2 buffer layers has been found to considerably affect the structure and magnetic properties of Sn1-xCoxO2 films. As the buffer-layer thickness increases, the lattice constant a and Co-O bond length of the Sn1-xCoxO2 films contract, which suggest the gradual relaxation of the accumulated tensile strain. Simultaneously, the amount of structural defects in Sn1-xCoxO2 films decreases significantly and the grain size increases with increasing buffer-layer thickness. All the Sn1-xCoxO2 films exhibit intrinsic ferromagnetism at room temperature and the saturated magnetic moment varies with the buffer-layer thickness. The dependence of ferromagnetism on the buffer-layer thickness can be explained on the basis of the variations in the density of structural defects and Co-O bond length in Sn1-xCoxO2 films.