Sputter-deposition of Co-Cr-Ta alloy layers on Ni-Zn ferrite plated underlayers

The influence of Ni-Zn ferrite plated underlayers on grain size and magnetic characteristics of sputter-deposited Co-Cr-Ta layers was investigated. These properties were found to be strongly influenced by the surface texture of the underlayers. When the grain size of the underlayers was large (200-300 nm), the grains in the Co-Cr-Ta layers seemed to aggregate and were not isolated clearly. When the grain size of the underlayers was small (50-70 nm), the grain size in the Co-Cr-Ta layers decreased and the perpendicular coercivity increased to over 2 kOe. Further studies showed RF sputter-etching of the underlayers reduced grain size (30~50 nm), and increased perpendicular coercivity (3.0 kOe), presumably through a reduction of surface roughness and a formation of many fine nodules on the underlayers, which play a role of nucleation sites for the Co-Cr-Ta grains