Application of Electroless Cobalt Alloy Thin Films to Perpendicular Recording Media

Perpendicular magnetic recording media by means of electroless plating method were studied and developed. A plating bath A composed of ammoniacal malonate-malate complexing agents was initially developed by deciding the optimum conditions according to the effects of three main factors: concentrations of MnSO₄ and NiSO₄, and pH of the bath on the magnetic properties and crystal structure of the Co alloy-thin films obtained. Secondly, the bath composition was further optimized for CoSO₄ concentration, NaH₂PO₂ concentration and bath temperature to obtain the revised bath B. The magnetic film plated from the bath B showed the lower coercivity Hc (⊥) and hence may be applied with the head having the narrower gap length for achieving the higher recording density. The films plated from the baths A and B were both composed of columnar structure of hep crystal with 0.05 μm diameter. It was observed that the grains were highly-oriented with a narrow dispersion of c-axis orientation normal to surface plane according to the rocking curve method. As a result of preparation of disks plated from baths A and B, the di-pulse waveforms which are characteristic of the perpendicular recording were observed at low bit recording density. The recording densities of D₅₀ = 18500 FRPI and 25000 FRPI were obtained respectively for the disks when used with the ring-type head and the improved ring head having the narrower gap length.