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 similar to 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 similar to 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 similar to 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.