APFIM study of the compositional inhomogeneity of sputtered CoCr magnetic thin film

An atom probe field ion microscope investigation has been performed to study the decomposition in Co-20at%Cr magnetic recording material. The measurements demonstrate the existence of a decomposition on a one nanometer scale. The concentration of these small clusters varies between 11 at% Cr and 42 at% Cr within at room temperature sputtered films. In films sputtered at 200°C the concentration varies from about 10 at% Cr to 30 at% Cr. Additionally, Cr-enriched precipitates at grain boundaries and concentration variations on a 8 nm scale were found. Annealing the samples at 750°C for 24 h leads to an almost homogeneous alloy. The measured concentrations in the sputtered samples depend on substrate temperature, respectively on annealing temperature. They are interpreted by a calculated miscibility gap in the hcp phase solid solution which is induced by magnetism at low temperatures.