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 electroless plating method, and the effect of film thickness on magnetic properties and recording characteristics was investigated. 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_k) and the perpendicular coercivity Hc(⊥)decreased with decreasing film thickness, and suitable magnetic properties could not be maintained for films thinner than 0, 2 μm. However, in the case of Co-Ni-Re-P alloy films, the values of H_kH_c(⊥), and perpendicular anisotropy energy (K_u) increased with decreasing film thickness, and magnetic properties suitable for perpendicular recording were obtained in the thinner films. The limiting recording density of D₅₀ increased with decreasing film thickness, and D₅₀ = 60 kFRPI was observed for a disk with a 0.05 pm thick Co-Ni-Re-P alloy film in combination 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 μm film thickness. It is suggested that electroless 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.