Evidence for microstructural inhomogeneity in sputtered Co-Cr thin films

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Abstract
Thin films of the perpendicular recording material Co100−xCrx(x=17–23) were ion beam sputtered from alloy targets. The saturation magnetization and uniaxial anisotropy constant, as a function of temperature, both show a strong dependence on the substrate temperature during deposition Ts, indicating composition shifts which increase with Ts. The films have a columnar structure on a scale which does not depend on Ts in contrast to the grain size. From studies of the phase relations in bulk Co‐Cr alloys and diffusion couples it is concluded that phase separation of ordered Co‐Cr phases does not occur at high Ts. Instead the composition shifts and the grain refinement at higher Ts are proposed to be caused by oxygen gettering and oxide trapping during film growth.