Effect of Film Thickness on the Magnetic Properties of Electroless Cobalt Alloy Plating Films for Perpendicular Magnetic Recording Media

Co-Ni-Re-Mn-P and Co-Ni-Re-P alloy films for perpendicular magnetic recording media were prepared by an elec-troless plating method, and the effect of film thickness on magnetic properties and recording characteristics was inves-tigated. This effect was found to differ greatly for the two alloy systems. In the case of Co-Ni-Re-Mn-P alloy films, the perpendicular anisotropy magnetic field (H~) and the perpendicular coercivity Hc(~-) decreased with decreasing film thickness, and suitable magnetic propert ies could not be maintained for films thinner than 0,2 ~m. However, in the case of Co-Ni-Re-P alloy films, the values of Hk, He(~-), and perpendicular anisotropy energy (Ku) increased with decreasing film thickness, and magnetic properties uitable for perpendicular recording were obtained in the thinner films. The l imit ing recording density of D.50 increased with decreasing film thickness, and Ds0 = 60 kFRP I was observed for a disk with a 0.05 ~m thick Co-Ni-Re-P alloy film in combinat ion with a ring head. The relationship between recording current and reproduced voltage for perpendicular recording was also measured in the thin medium thickness range for Co-Ni-Re-P alloy films, and the typical behavior for perpendicular magnetic recording was confirmed in the thinner 0.05 ~m film thickness. It is suggested that e]ectroless Co-Ni-Re-Mn-P alloys are suitable for single-layer media and that Co-Ni-Re-P alloys are suitable for composite anisotropy media. Since the proposal of Iwasaki (1) in 1977, much effor