The effect of an underlayer on recording characteristics was investigated for electroless plated perpendicular recording double layer media. Various double layer media were fabricated by plating 0.1μm thick CoNiReP recording layer onto several kinds of Ni alloy underlayers of 0.05μm thick. A higher reproduced voltage was observed for the medium with a softmagnetic NiFeP underlayer. The effect is called ‘double layer effect.’ Although both the media with a NiWP and a NiP(pH10) underlayers showed almost the same magnetic properties, a higher reproduced voltage at a high densities appeared for the medium with a NiWP underlayer. It turned out to be due to a higher crystallinity of the recording layer for the NiWP double layer. This effect to improve a crystallinity of recording layer is underlayer effect. The quasi-softmagnetic NiWP underlayer has two effects. So the highest D50 value of 152kFRPI with a video ring head was obtained for the medium of CoNiReP/NiWP to show a high potential of electroless media.
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