The structure and properties of sputter-deposited Co-Si alloy thin films

The structural and magnetic properties of Co1-xSix alloy thin films in the composition range 0 < x < 0.9 are investigated. The sputter-deposited thin films show a single phase hcp structure up to x similar to 0.25. For Si compositions beyond this, but with x < 0.6, electron diffraction implies a single amorphous phase with features in the diffraction patterns typical of a dense random packing of hard spheres (DHRPS). These alloys are ferromagnetic. For 0.6 < x < 0.8 additional diffraction maxima are observed that suggest the formation of at least two amorphous phases. Magnetic measurements suggest the presence of thermally unstable magnetic particles. For x > 0.7-0.8, Co atoms are incorporated in the covalent random network structure of Si and paramagnetism is observed. A correlation of the PEELS Co L-2/L-3 edge loss intensity ratio with the effective Co moment suggests that the magnetic changes could arise from differing local environments as Si is added, rather than a change in the particle size. Compositional mapping shows that some of the films have a composition that is not spatially uniform.