The addition of small amounts of tartronic acid was found to improve the perpendicular magnetic anisotropy of Co-Ni-Re-Mn-P alloy films, and the increased anisotropy energy Ku was explained by the constant Hk with decreasing Ms. The addition of tartronic acid up to 0.05mol dm
-3, was observed to bring about an increase in the Ni and P content, accompanied by a decrease in Co content. Differences in magnetic properties were not observed between electroless Ni-P and activated copper substrates at various tartronic acid concentrations; but differences were observed in the lower NiSO
4 concentration region. Read/write characteristics were tested using 8-inch disks plated with Co-Ni-Re-Mn-P alloy under optimum conditions in combination with ring head having a 0.33μm head gap. Dipulse waveforms, which are characteristics of perpendicular magnetic recording, were observed in the long wavelength and recording density D
50=58kFRPI was obtained at 0.20μm head-to-medium spacing.
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