The effect of initial growth layer on magnetic properties of Co-Cr films

The effect of a Ti underlayer, which increases the perpendicular coercive force of Co-Cr films, was investigated. To clarify the cause of this phenomenon, the film-thickness dependence of the magnetic properties was examined. It was found that the coercive force of a Co-Cr film deposited directly on a polymide substrate decreases drastically when it becomes thinner than 50 nm, whereas in the case of Co-Cr film on a Ti underlayer, a high coercive force is maintained even when the film becomes as thin as 20 nm. The film with the underlayer has a distinct uniform columnar structure, whereas the film without it has a 50-nm-thick initial growth layer with no clear structure. Measurements of the temperature dependence of magnetic properties and observations of segregated microstructures indicate that the improvement of magnetic properties by the insertion of the Ti underlayer is mainly due to the improvement of shape anisotropy resulting from the formation of a distinctly segregated microstructure