Media noise reduction in Co-based longitudinal media with new Co co-precipitated NiP/Al substrate

To decrease the grain size and grain size distribution in longitudinal media, a small amount of oxygen exposure onto either normal NiP or Co co-precipitated Co-NiP/Al-alloy substrates has been used. The substrate surfaces of both media were dry-etched by RF-plasma prior to oxygen exposure. The exposure of 3.5 L of oxygen onto the normal NiP substrate surface reduces the grain diameter from 10.0 nm to 8.8 nm while maintaining the standard distribution of grain diameter of about 1.4 nm. As a result, the media signal to noise ratio increases by 0.6 dB. By adding 400 ppm of Co into NiP plated substrate and combined with 1.5 L of oxygen exposure, the grain diameter and the standard distribution of grain diameter decrease from 9.2 nm to 8.3 nm. As a result, the media signal to noise ratio increases by 1.0 dB.