Control of Thickness Dependence of Perpendicular Coercivity on Electroless Co—Ni—Re—P Alloy Thin Films

Electroless Co alloy films for use as perpendicular magnetic recording media were investigated with respect to the thickness dependence of their magnetic properties. The read/write characteristics, especially the dependence of the overwrite on the recording density, were very different for Co-Ni-Re-Mn-P films and Co-Ni-Re-P films. Since those films displayed different thickness dependences of perpendicular coercivity Hc (⊥), efforts were made to control the thickness dependence of the Hc(⊥) of Co-Ni-Re-P alloy films. The thickness dependence of the Hc(⊥) of Co-Ni-Re-P alloy films can be easily controlled by adjusting the sodium malonate concentration in the plating bath. When films are very thin, such as 0.1 µm thick, the Hc (⊥) value and degree of c-axis orientation increased with increasing sodium malonate concentration. However, when the film thickness was increased to 0.5 µm, these properties were nearly the same for different sodium malonate concentrations.