Compositional separation in Co-Cr based thin film magnetic recording media

Since Co is ferromagnetic and Cr is not, compositional inhomogeneities are believed to play an important role in determining the magnetic and recording properties of Co-Cr based thin film magnetic recording media. By preferentially etching Co-enriched regions in a Co-Cr film we discovered a “Chrysanthemum-like Pattern”, suggesting the presence of very fine, periodic compositional variations within individual grains. Subsequent studies, including thermo-magnetic analysis, nuclear magnetic resonance and atom probe field ion microscopy revealed the existence of a Compositional Separation (CS) in these films, producing distinct Co-enriched and Cr-enriched compositional phases. More recently, neutron scattering experiments have provided evidence of a magnetic microstructure with features matching the scale of the Co-enriched regions. Further investigations of this phenomenon are expected to open up new areas of research in both magnetic recording and thin film metallurgy. We review our study of CS, explain control of the compositional distribution using film growth parameters and discuss possible origins of CS.