Structural Control of Electroless-Plated Magnetic Recording Media by Underlayers

The structural control of electroless-plated CoP film was investigated using underlayers of electroless-plated CoNiMnP and CoNiP films. The CoNiMnP film showed a high degree of orientation of the hcp Co c-axis normal to the film plane, whereas the CoNiP film hardly showed any preferred orientation. The CoP film plated onto the CoNiMnP underlayer showed a high degree of preferred orientation, while the CoP film plated onto the CoNiP underlayer showed a low degree of preferred orientation. Thus, the microstructure of the CoP film is clearly influenced by the underlayer structure. In the case of the CoP film onto the CoNiMnP underlayer. an epitaxial-like growth was observed up to a thickness of 0.25 μm, and this reduced to the intrinsic microstructure at a thickness of 0.5 μm. Recording characteristics were measured on the 5 in. flexible disks, fabricated by plating the high-oriented CoP film or the low-oriented CoP film with a ring-type head of a commercial VHS video head. Perpendicular recording was performed on the high-oriented CoP film to demonstrate the best characteristics. The use of an oriented underlayer is thus confirmed to be a useful method of controlling the structure of the magnetic film in addition to controlling the bath plating parameters.