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

The effect of a Ti underlayer on the magnetic properties of Co-Cr films was investigated. Although the existence of a Ti underlayer does not improve the crystallographic orientation of Co-Cr films, it increases their perpendicular coercive force. In order to clarify the cause of this phenomenon, the film thickness dependence of the magnetic properties of Co-Cr films was investigated. As a result, it was revealed that the coercive force of a Co-Cr fails deposited directly on a polyimide substrate decreases drastically when it becomes thinner than 50nm, whereas in the case of Co-Cr film on a Ti underlayer, a high coercive force is maintained even when it becomes as thin as 20nm. According to our observation of cross-sectional structures, the Co-Cr film with the Ti underlayer has a distinct uniform columnar structure, whereas the Co-Cr film without the Ti underlayer has a 50nm thick initial growth layer which has no clear structure. Moreover, according to the measurements of temperature-dependence of magneticproperties and observations of segregated microstructures in Co-Cr films, it was found that the improvement of magneticproperties by the insertion of the Ti underlayer was mainly due to the improvement of shape anisotropy which was caused by forming a distinctly segregated microstructure.