The composition, structure and optical properties of weakly magnetic Co-containing amorphous Si and Ge films

► a-SiCo and a-GeCo thin films have been deposited by rf sputtering. ► The Co atoms were effectively and homogeneously incorporated into the amorphous hosts. ► Thermal treatments induce the crystallization of the samples and the formation of non-magnetic secondary phases in the films containing Co. ► The optical properties of the films are significantly affected by the insertion of Co and by the temperature of thermal annealing. ► The samples exhibited reduced magnetic signal at room temperature.