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.
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