An attempt on control of perpendicular coercivity toward film thickness direction of electroless plated cobalt alloy films for perpendicular magnetic recording

Electroless plated CoNiReP alloy films with perpendicular magnetic anisotropy were studied from the standpoint of controlling the magnetic properties at the very thin initial deposition stage. Thickness dependence of perpendicular coercivity, Hc(┴), was easily controlled by adjusting the sodium malonate concentration in the bath. The higher sodium malonate concentration made the Hc(┴) values at the 0.1 µm thick initial deposition stage higher, however at thickness greatar than 0.5 μm the Hc(┴) values were almost the same independent of sodium malonate concentration.Recording performance on these disks was evaluated by using Winchester ring-heads under 0.17 μm head-medium spacing. D50 values somewhat depended on the sodium malonate concentration, and 0.25 μm thick disk plated at 0.50 mol/l sodium malonate gave the highest D50 value of 64 kFRPI using an 0.23 µm gap length head. Overwrite values were affected by the sodium malonate concentration, and the highest values of -30 dB was attained at the 0.25 µm disk plated at 0.30 mol/l sodium malonate using 0.53 pm head gap length. Medium having the lower Hc(┴) at the initial deposition stage made the preferable conditions for the read/write characteristics, especially overwrite, of perpendicular recording when using the system of combining a Mn-Zn ferrite ring-head.