CoCrPtO-Based Granular Composite Perpendicular Recording Media

The effect of capping layer thickness (t
_Cap
) on media properties in CoCrPtO-based granular composite media is investigated. The CoCrPt-based capping layer with much less coercivity (H
_c
) and more exchange coupling than the bottom layer was used. Surprisingly, H
_c
increases from 4.9 to 5.9 kOe with increasing t
_Cap
from 0 to 3.8 nm (Zone I) and then decreases to 4.1 kOe at t
_Cap
=8.3 nm (Zone II). As t
_Cap
increases, the a axis lattice constant increases from 2.584 to 2.592 Aring, while the c axis lattice constant decreases from 4.213 to 4.192 Aring. Zone I exhibits relatively constant loop slope (alpha) at H
_c
and activation volume (Vact) for magnetic reversal, while Zone II shows the increase in alpha and V
_act
. This increase is confirmed by TEM images with less grain isolation and larger grain size. Angular dependence of H
_cr
in Zone II shows less coherent switching behavior compared to Zone I. Thermal stability factor continuously improves from 59 to 107 with increasing t
_Cap
. Simulation results reveal that the increase in H
_c
at Zone I is mostly due to the enhancement of thermal stability. The decrease in H
_c
at Zone II is understood as a dynamic tilted medium caused by the increase in lateral exchange coupling in the capping layer