Effect of Magnetic Recording Layer Thickness on Media Performance in CoCrPt-Oxide Perpendicular Media

The microstructure, magnetic properties, and recording performance of CoCrPt-oxide perpendicular media were investigated at different magnetic layer film thicknesses (t
_MAG
) from 2 to 27 nm. Media coercivity (H
_c
) reached a maximum value of 6.8 kOe at t
_MAG
= 18 nm and then decreased to 5.3 kOe. Both crystallographic and magnetic c-axis orientations remained constant in the film thickness range of 12-27 nm. The change in the degree of grain isolation and grain size was observed as t
_MAG
increased. Higher exchange coupling at t
_MAG
= 4 nm was observed due to less grain isolation, but the in-plane magnetization was not detected. At t
_MAG
= 10-18 nm, excellent grain isolation was achieved. However, the formation of many subgrains and less grain isolation at t
_MAG
= 27 nm was related to the reduced H
_c
. When t
_MAG
increased to above 12 nm, media signal-to-noise ratio rapidly decreased because of significant increase in dc-erase media noise, even though no degradation of media properties was observed up to t
_MAG
= 18 nm. The significant increase in the dc-erase noise is related to poor media writability, contributed by both the increase in H
_c
and the reduction in head field magnitude, caused by increasing head-to-soft magnetic underlayer distance