Compositional inhomogeneities in sputtered Co-Cr magnetic thin films studied by atom probe field ion microscopy

Compositional inhomogeneities in Co-22 at. % Cr sputtered thin films have been studied quantitatively using atom probe field ion microscopy. For comparison, a Co-22 at. % Cr bulk alloy specimen has also been examined. As predicted from the recently published phase diagram, a solution treated Co-Cr bulk alloy specimen does not contain detectable chemical inhomogeneities. On the other hand, the Co-22 at. % Cr thin film sputter deposited at 200 °C consists of two distinct phases with different Cr concentrations. The size of each phase is in the order of 8 nm which is significantly smaller than the grain size of the specimen; however, the film that was sputter deposited at ambient temperature exhibited a significantly lower level of compositional inhomogeneity. Based on these results, it is concluded that the phase separation progresses when thin films are deposited on heated substrates.