Effects of NiP underlayers on recording characteristics of electroless Co alloy perpendicular magnetic recording media.

The double layer effect of an electroless plated CoNiReP alloy medium in combination with an electroless plated NiP underlayer was investigated by a system consisting of a flexible disk with a VTR ring head (gap length 0.3-0.4μm). The underlayer of NiP improved the recording characteristics and the D50 changed from 76kFRPI (single layer) to 85kFRPI (double layer). When using a pH6 NiP underlayer of amorphous state, even the addition of a film only 0.03μm thick effectively improved the output voltage. The increase in the thickness of the underlayer made the second peak of higher recording density clear. When using a pH 10 NiP underlayer of quasi-soft magnetic crystalline state, the same improvement was observed, and an additional increase in output voltage due to the so-called “double layer effect” was observed even at a thickness of 0.03μm. In contrast to the pH 6 NiP underlayer, the improvement at higher recording density by underlayer addition was reduced as underlayer thickness increased. The above results were discussed from the viewpoint of variations in magnetic medium structure.