The perpendicular magnetic recording performance of electroless CoNiReP/NiFeP double-layered media using ring- type heads was investigated, focusing upon the recording processes and the effect of underlayer coercivity (.Hc(u) = 5 ~ 160 Oe). For the recording on medium whose Hc(u) value is higher than several tens of Oe, the underlayer is also magnetized by a head field, and the phase of such a longitudinal magnetization of the underlayer is shifted in proportion to the change of magneto-motive force (MMF). In the low MMF region, the phases of perpendicular transition and longitudinal transition are synchronized, forming the horseshoe mode through the perpendicular layer and the underlayer. Consequently, the output voltage, by maintaining single-peak shaped signals, drastically increased by the so- designated “phase synchronization” effect. Greater improvement of reproduced voltage by such a phase synchronization effect was obtained for the higher Hc(u) medium.
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