Electroless plated Co-Ni-Re-P alloy films for perpendicular recording medium were investigated and developed. It was found that the addition of tartronic acid into the plating bath makes it possible to form the Co-Ni-Re-P perpendicular anisotropy films with noMnSO4 present. The Co-Ni-Re-P alloy film whose composition is simpler than that of the previously developed Co-Ni-Re-Mn-P films, has a higher potential than that of Co-Ni- Re-Mn-P alloy film from a practical use viewpoint as a perpendicular recording media. Readlwrite characteristics of 8 inch disks using Co-Ni-Re-P medium were also obtained and measured with a combination of a ring head. Characteristics whose quality was almost equal to those of Mn codeposited media were obtained, and a higher recording density would be expected with improvement in the matching condition between head and disk properties. The recording density of 54 kFRPI as D50 was obtained with 0.02 μm thick magnetic medium using a 0.33 μm gap length ring head at 0.12 μm head-medium spacing.
