Segregated microstructure in sputtered Co-Cr film revealed by selective wet etching

Abstract

The segregated microstructure in a sputtered Co-18.1 at. % Cr film is examined. Thin foil samples are prepared for transmission electron microscopy using selective wet etching and ion-beam milling. The microstructure revealed by selective wet etching shows a definite striped pattern in each crystallite where the stripes run almost perpendicular to grain boundaries. Results of compositional analysis by an energy dispersive x-ray microanalyzer reveal that these stripes are caused by dissolution of the Co-rich ferromagnetic regions and that the remaining regions are Cr-rich and nonmagnetic. The results are explained by a new model for segregated microstructure formation. Ferromagnetic Co-rich regions are formed coherently in each single-phase hcp crystallite, with a wall-like structure perpendicular to the substrate plane. The observed microstructure suggests the existence of a magnetic unit far smaller than the crystallite diameter, which offers superior properties for high-density perpendicular magnetic recording.